Calipers on an automobile typically refer to the vehicle's brake calipers, which are mechanisms that control the movement of brake pads. The brake caliper is an integral part of the common disc brake system.
A disc brake system works to slow a vehicle down via friction. A pair of brake pads is squeezed against the surface of a brake rotor, effectively converting the kinetic energy of the vehicle into heat energy. The brake caliper is the mechanism that houses the brake pads and uses hydraulic energy to engage the pads when the brake is engaged. Disc brake systems have largely supplanted drum brake systems in many vehicles, as the brake caliper locations allow for better ventilation and cooling of the brake system.