Footstools, foot rests, and ottomans are, as the name implies, cushioned rests for your feet while you are seated. Usually, a footstool is part of a two-piece furniture set with a chair such as an armchair.
Footstools are usually padded in some way to provide comfort. Typically, cushion foam lies under leather or faux-leather upholstery, sometimes under fabric instead. Some ottoman-style footstools serve as storage chests, with a compartment under the cushioned lid where the feet rest.