Glossary of Terms Related to Child Restraint Systems

3-point harness – A harness found on infant-only restraints consisting of shoulder straps coming together at a buckle in the shell or on a crotch strap; not to be confused with 3-point (lap-shouldervehicle belts.

5-point harness – A CR harness that has a webbing strap over each shoulder, one on each side of the pelvis, and one between the legs, with all five coming together at a common buckle.

5-Step Test – A test to determine whether or not a child is tall enough to have the seat belt properly fit in a given vehicle.

Acceleration – A measure of how fast a body (mass) gains or loses velocity as the result of a force being applied to that body.

Aftermarket products – Products such as toys, inserts, covers, or anything added to a child restraint (cr) but not specifically approved for use by the CR manufacturer.

Air bag – Air bags come in a variety of forms, but their purpose is always to spread crash forces over a wider area of an occupant’s body during a crash, thus reducing injury. Air bags also assist with ride down – helping the occupant to take a longer time to come to a stop. Air bags are engineered for adults and are meant to be used in conjunction with safety belts.

Anchor – A common short alternative for anchorage; often used to refer specifically to the hardware installed at the anchorage, either factory-installed or in a retrofit shoulder-belt or tether kit.

Anchor bar – A common alternative for lower anchorage.

Anchor point – A location identified in a vehicle where anchorage hardware, usually for a retrofitted top tether anchorage, may be installed.

Anchor– A strong point and associated hardware in a vehicle to which a vehicle belt or LATCH attachment is secured. See Adjustable upper anchorageChild restraint anchorage systemLATCH anchorageLower anchorageTop tether anchorageUpper anchorage.

Anti-rebound bar – Found on some rear-facing safety seats, its purpose is to limit movement of the safety seat toward the rear of a vehicle during a crash.

Automatic locking retractor (ALR) – A vehicle belt retractor that allows the belt to be pulled out initially but locks when the pull-out action stops and tension is again applied. See also Emergency locking retractor,Switchable retractor.

Backless booster – A type of booster, as defined by FMVSS 213, that has a seating platform and a structure in front of the child for restraint, but which is subject to crash testing using only a lap belt and to the head excursion limit of only 813 mm.

Belt – See Vehicle belt.

Belt-positioning booster (BPB) – A firm platform, used with a lap-shoulder belt, that raises the child so that the height of his thighs and shoulders are closer to those of an adult and helps route both portions of the lap-shoulder belt to fit the smaller body; can be backless or have a high back, usually with a shoulder belt guide. See also Combination seats.

Belt-shortening clip – Metal hardware used to fix the length of a lap belt with emergency-locking retractor, by securing a loop of belt from slipping through the clip; formerly called a “heavy-duty” locking clip. See also Locking clip.

Bight – See Seat bight.

Built-in child restraint system – A CR designed to be an integral part of and permanently installed in a vehicle.

Car bed – An infant restraint that allows the baby to lie flat, with the long axis of the child’s body perpendicular to the direction of travel and head away from the door, the primary restraint surface being the side of the bed; primarily used with low birth weight infants and those with special medical needs.

Car seat – A common alternative term for child restraint system, especially when speaking with general audiences; easily confused in written material with “vehicle seat,” unless spelled as one word: “carseat.”

Chest clip – See Harness retainer clip.

Child restraint anchorage system – A standardized system of user-ready hardware in vehicles, consisting of two lower anchorages and one upper anchorage specified in FMVSS 225, for installing child restraint systems independent of the vehicle seat belt; referred to as LATCH in the U.S. and similar to the Canadian Lower Universal Anchorage System.

Child restraint system (CRS or CR) – A general term in FMVSS 213 for a device designed “to restrain, seat, or position children who weigh 50 pounds of less” used primarily with professional and technical audiences. This applies to any new seat sold in the US, including booster seats and special needs seats. Manufacturers self-certify that their products meet SMVSS 213 performance standards.

Child safety seat (CSS) – A common alternative term for child restraint system used primarily with general audiences.

Cinching latchplate – A latchplate on a lap-shoulder belt that will meet the “lockability” requirements of FMVSS 208 but will allow the belt to slip during a crash, making it necessary to remove all slack from the shoulder portion of the belt when used to secure a CR. See also Locking latchplate.

Combination seat – A forward-facing CR or child seat that has a removable harness and can also be used as a belt-positioning booster.

Connector – Hardware at the end of a LATCH attachment, such as a top tether hook specified in FMVSS 213 or other latching device compatible with lower anchorages specified in FMVSS 225, that enables the CR to be securely fastened to a LATCH anchorage; can be either a hook-on connector or a push-on connector (lower attachments only).

Convertible child restraint – A CR that can be used rear-facing for infants up to at least one year and 22 lbs. or as much as 50 lbs., and then turned to face forward until the child reaches the upper weight limit, at least 40 lbs., but mostly much higher, of the product.

Dynamic Locking Latchplate – Similar in appearance, but not function, to a locking latchplate, a dynamic locking latchplate locks the lap portion of the safety belt only during a crash, and thus cannot be used to secure a child restraint. If installing a child restraint in a seating position with a dynamic locking latchplate, the retractor must be locked.

Emergency-locking retractor (ELR) – A vehicle belt retractor that locks only when the vehicle stops suddenly, often including sudden braking. See also Switchable retractor.

Flexible attachment – A lower attachment that includes webbing and usually a manual length adjuster that is manually tightened.

Forward-facing-only child restraint – A safety seat with a harness system that may be used forward facing only, different from a combination seat in that a forward-facing-only seat cannot be converted to a booster.

Funnel guide – A device incorporated with some LATCH system lower anchorages to help the user position and guide the lower attachment connector during CR installation.

Harness – The webbing assembly attached to a CR shell or frame that restrains the child in a crash; also an independent restraint system made entirely of webbing (with fasteners and length adjusters), often referred to as a “child harness,” and subject only to the head excursion limit of 813 mm.

Harness retainer clip – A plastic or fabric device that holds the shoulder straps of a harness in place on the child’s chest for pre-crash positioning; not required, defined, or regulated by FMVSS 213; also called a “chest clip.”

Head excursion – The distance that the head of a child or crash dummy moves in the direction of impact or on rebound from a crash; regulated forward limit for most forward-facing CRs, measured from the test bench pivot point, of 813 mm (no top tether allowed) and 720 (top tether allowed).

Head Injury Criterion (HIC) – A calculated value, using a complex formula related to the magnitude and duration of dummy head acceleration, with or without direct head impact, that indicates the likelihood of serious head injury.

Heavy-duty locking clip – See Belt-shortening clip.

Hook retainer spring – The leaf spring that closes the opening in a hook-on connector or top tether hook.

Hook-on connector – A top tether hook, or hardware at the end of a lower attachment that resembles such a hook.

Inflatable Seat Belt – The shoulder portion of this safety belt contains an air bag which spreads crash forces over a greater area of the occupant’s body during a crash. Many CR manufacturers do not allow use of inflatable seat belts with their products. Ford, the initial manufacturer, has ceased using this technology as of 2020.

Integrated CR – See Built-in child restraint system.

ISOFIX – A system for the connection of a CR to a vehicle that has two lower anchorages in a vehicle seating position located near the seat bight, corresponding rigid attachments on the CR, and a means to limit the pitch rotation of the CR; defined by ISO 13216-1 and adopted by European countries; differs from LATCH and LUAS in that only rigid attachments are allowed and top tethers are not required.

Lap belt – A vehicle belt that restrains the lower torso (pelvis); may be a lap-only belt or a portion of a lap-shoulder belt; referred to as a Type I belt system in FMVSS; can be used to secure a CR.

Lap-shoulder belt – A vehicle belt that restrains both the lower and upper torso, usually with a continuous loop of webbing connected to a buckle with a latchplate; referred to as a Type II belt system in FMVSS; can be used to secure a CR; term may be substituted by the phrase “lap and shoulder belt” in instructions and other communications on routing and use to emphasize both segments of the belt.

LATCH – An acronym that stands for “Lower Anchors and Tethers for CHildren” and refers to the child restraint anchorage system specified in FMVSS 225 and the corresponding top tethers and lower attachments identified in FMVSS 213. See also ISOFIXLower Universal Anchorage System.

LATCH anchor – Hardware in the vehicle to which a top tether or a lower attachment is connected as part of a complete CR installation.

LATCH attachment – A hardware assembly on a CR, possibly including webbing, that connects to a top tether anchorage or a lower anchorage as part of a complete CR installation. See also Connector.

Latchplate – The metal portion of the vehicle belt assembly that connects to the buckle and through which the webbing is threaded; the insertion tip is also called the “tongue.” See Free-sliding latchplateCinching latchplateLockabilityLocking latchplateSwitchable latchplate.

Load Leg – Extends from the base of the safety seat to the vehicle floor, adding stability and reducing the transfer of crash forces to the child occupant. Found primarily on rear-facing-only seats in the U. S.

Lock-off – A clamp attached to the CR that is affixed to the vehicle belt to maintain tension on the belt, to prevent movement of the webbing relative to the latchplate and/or to prevent movement of the CR relative to the webbing; may be used in place of a locking clip with a lap-shoulder belt or, in a few U.S. rear-facing models, with a lap-only belt to improve lateral stability and coupling to the vehicle; defined in ECE R44.03 as “a device which locks and prevents movement of one section of the webbing of an adult safety-belt relative to another section of the webbing of the same belt” and is applicable both to CR installation and to belt-positioning booster use.

Lockability – Beginning with the 1996 model year, a regulated feature requiring that the lap portion of a vehicle belt “can be used to tightly secure a child restraint system” without “any device that must be attached by the vehicle user to the seat belt webbing, retractor, or any other part of the vehicle,” and “shall not require any inverting, twisting or otherwise deforming of the belt webbing” (FMVSS 208, S7.1.1.5).

Locking clip – Metal hardware used to hold the lap portion of a lap-shoulder belt from lengthening during normal driving by clamping the webbing together next to the latchplate; also called a “regular” locking clip. See also Belt-shortening clip.

Locking latchplate – A latchplate on a lap-shoulder belt that, when buckled, will allow the lap portion to be pulled into the shoulder portion but will restrict its slippage back to the lap belt; a latchplate on a lap-only belt that restricts slippage once the belt is buckled and pulled tight; meets the “lockability” requirements of FMVSS 208.

Lower anchor – One of two horizontal rigid bars 6 mm in diameter and 25-40 mm long specified in FMVSS 225, installed in vehicles in or near the seat bight, and to which one of two lower attachments is connected to secure the lower part of the CR. See also Child restraint fixture (CRF)Funnel guideLATCH anchor.

Lower attachment – One of two hardware assemblies on the CR, possibly including webbing (or a single assembly with a connector at each end) that enables the CR to be securely fastened to one of two (or both) lower anchorages. See also LATCH attachments.

Lower connector system – Term used in Transport Canada regulations for lower attachment.

Lower tether – A strap and hardware assembly attached near the back and base of a large rear-facing CR and attached to the vehicle seat track or other low anchorage to restrict rotation of the CR toward the rear of the vehicle; used primarily in Scandinavian markets. Eliminated in the U.S. due to computerized assessments of air bag deployment for front seat occupants and potential interference in computerized responses.

Lower Universal Anchorage System (LUAS) – Term used in Transport Canada regulations for a system similar to LATCH

Misuse – Any deviation from the intended application and use of a CR that might reduce its protective performance.

Push-on connector – Hardware at the end of a lower attachment, usually with a spring-loaded latch, that automatically locks around the rigid bar when pushed onto a lower anchorage.

Pushbutton adjuster – A strap adjustment mechanism that releases its hold on the webbing for the purpose of lengthening the strap when a button is depressed; does not inhibit the strap from being shortened when the free end of the webbing is pulled.

Rear-facing-only child restraint – A restraint system that only faces the rear of the vehicle, traditionally has a back height (rump to top of shell) of 18″ or 20″, and is generally limited to children weighing  20 – 40 lbs.

Recline adjustment mechanism – a device built into the safety seat to assist with achieving proper recline in rear-facing or forward-facing mode.

Recline indicator – Indicates correct recline of safety seat per CR manufacturer’s instructions.

Rigid attachment – One of two hardware assemblies, built into the CR base at 280mm apart, that meet the requirements of ISO 13216-1 and are used to connect a CR to a lower anchorage; a lower attachment also allowed in LATCH and LUAS.

Safety belt – See Vehicle belt.

Seat belt – See Vehicle belt.

Seat belt syndrome – Injuries that result from improper lap belt fit on a child i.e., a lap belt on the abdomen or stomach vs. on the upper thighs. Injuries include but are not limited to crushed liver, crushed spleen, other severe abdominal injuries, and spinal injuries.

Seat bight – The intersection of the vehicle seat back and bottom cushions, where vehicle belts frequently emerge and where or near where lower anchorages are placed.

Sewn-on latchplate – a latchplate that is sewn on to the end of the safety belt webbing.

Shell – The molded plastic structure of a CR that positions the child in the harness and is either strong enough by itself to provide impact protection or, in some models, is reinforced with a metal frame.

Shoulder belt – A vehicle belt that restrains the upper torso; is most commonly a portion of a lap-shoulder belt, but may be a shoulder belt alone in some older vehicles; the latter cannot be used to secure a CR.

Shoulder belt guide – A slot, hook, loop, or clip attached to the side of a highback belt-positioning booster, or a clip on an adjustable strap attached to a backless BPB, through which the vehicle shoulder belt is routed to help place and keep it crossing the shoulder between the child’s neck and arm.

Shoulder belt positioner – Built-in or aftermarket device that helps place and keep the vehicle belt crossing the shoulder between the neck and arm. See also Adjustable upper anchorage; also called a “comfort guide.”

Sliding latchplate – A latchplate on a lap-shoulder belt that does not impede belt  movement so it slides easily, changing the lengths of the lap and shoulder portions and therefore, does not meet the “lockability” requirements of FMVSS 208.

Submarining – The motion of an occupant when one or both hips slide under the lap belt, so that the belt applies crash forces to the soft abdominal area between the pelvis and ribs.

Switchable latchplate – A latchplate on a lap-shoulder belt that can be converted from a free-sliding to a locking latchplate for CR installation.

Switchable retractor – A vehicle belt retractor that can be changed from an emergency-locking retractor to an automatic-locking retractor for tight installation of a CR. See also Lockability.

Tether – A common short alternative for top tether.

Tilt-lock adjuster – A strap adjustment mechanism that releases its hold on the webbing for the purpose of lengthening the strap when the hardware is held at an angle relative to the webbing; does not inhibit the strap from being shortened when the free end of the webbing is pulled.

Top tether – An assembly consisting of a top tether strap, attached at or near the top of a CR, together with a length adjuster and a top tether hook, that is used along with either a vehicle belt or lower attachments for complete installation of a CR in a vehicle.

Top tether anchor – Hardware component, such as a ring, bar, bracket, or webbing loop, and its underlying structure in the vehicle, either user-ready or aftermarket-installed, to which a top tether is attached.

Top tether hook – A metal connector specified by FMVSS 213 to attach a top tether strap to a top tether anchorage.

Top tether strap – A straight or V-shaped length of webbing attached at or near the top of a CR as part of a top tether assembly.

Type I belt – See Lap belt.

Type II belt – See Lap-shoulder belt.

Upper anchorage – Term used in FMVSS 225 for top tether anchorage.

Vehicle belt – A webbing, buckle, latchplate, and length-adjustment (usually a retractor) assembly installed in the vehicle that is used to restrain an occupant or a CR; also called a “safety belt” or “seat belt”; may consist of a lap belt only, a combination lap-shoulder belt, separate lap and shoulder belts, or less commonly a shoulder belt alone with a knee bolster.

Vest – See Harness.


ECE R44-03, Uniform Provisions Concerning the Approval of Restraining Devices for Child Occupants of Power-Driven Vehicles (“Child Restraint System”), June 1998.

Federal Motor Vehicle Safety Standards

FMVSS 208, Occupant Crash Protection. 49 CFR 571.208. October 2003.

FMVSS 213, Child Restraint Systems. 49 CFR 571.213. October 2003.

FMVSS 225, Child Restraint Anchorage Systems. 49 CFR 571.225. October 2003.

ISO 13216-1. Anchorages in Vehicles and Attachments to Anchorages for Child Restraint Systems – Part 1: Seat Bight Anchorages and Attachments. March 2000.

ISO 13216-2. Anchorages in Vehicles and Attachments to Anchorages for Child Restraint Systems – Part 2: Top Tether Anchorages and Attachments. Draft May 2003.

National Highway Traffic Safety Administration. Child Occupant Protection Glossary. In National Standardized Child Passenger Safety Training Program – Instructor Guide, p. A-8 – A-14. 2004 (in press).

Stewart DD, Kern KC. LATCH…The Essential Guide. 11th ed. Safe Ride News Publications, Seattle, 2019.

SafetyBeltSafe U.S.A. Child Passenger Safety Technical Encyclopedia. 2004.

Transport Canada, Motor Vehicle Restraint Systems and Booster Cushions Safety Regulations (RSSR).

Transport Canada, Motor Vehicle Safety Regulations

Standard 210.1, User-Ready Tether Anchorages for Restraint Systems.

Standard 210.2, Lower Universal Anchorage Systems for Restraint Systems and Booster Cushions.