Canister lights are the recessed lights you see in kitchen ceilings. The bulbs are mounted up and inside the fixtures. Typically, you need about 10 inches above the "ceiling" in which to mount the fixture.

They are typically designed for up to 100W incandescent lamps, so any of the new led regular or spotlight bulbs would work perfectly, and use a lot less electricity and generate a lot less heat which normally shortens the life of the larger incandescent bulbs/