Prismatic joint
A joint that allows sliding along a single axis only — the mirror image of the hinge, which allows only rotation.
The prismatic joint, sometimes called a slider joint, locks all rotation and all translation except one: movement along a chosen axis. Of a rigid body's three degrees of freedom in 2D it leaves exactly one. A motor can drive the body along the axis and limits can stop it at either end.
The name comes from the motion being "prismatic" — straight-line, like a prism riding a rail. It models elevators, pistons, hydraulic cylinders, sliding doors and platforms that travel back and forth. Box2D and PhysX use the same term; some engines simply call it a slider.