Similar in usage to a shoe, a slipper is an indoors version along the same vein.
Shoes are generally made of canvas, plastic, or rubber. Boots are generally made out of either leather of a leatheresque synthetic compound, and have hard rubber soles.
Slippers are frequently made out of either felt or soft leather (which may or may not be lined with a soft material such as felt). Some slippers, particularly those meant to be used near pools, bathrooms, or other wet places, are made of plastic or rubber.
Slippers may be shaped like a shoe (foot inserted through top), or may have no heel, so the foot can be slipped in the back.
The term "slipper" is sometimes used interchangeably with the terms flip-flop and sandal.