A chair is a raised surface used to sit on, commonly for use by one person. Chairs often have the seat raised above floor level, supported by four legs. A chair without a back or arm rests is a stool, or when raised up, a bar stool. A chair with arms is an armchair and with folding action and inclining footrest, a recliner. A permanently fixed chair in a train or theater is a seat or airline seat; when riding, it is a saddle and bicycle saddle, and for an automobile, a car seat or infant car seat. With wheels it is a wheelchair and when hung from above, a swing.

The design may be made of porous materials, or be drilled with holes for decoration; a low back or gaps can provide ventilation. The back may extend above the height of the occupant's head, which can optionally contain a headrest.

A chair for more than one person is a couch, sofa, settee, or "loveseat"; or a bench. A separate footrest for a chair is known as an ottoman, hassock or pouffe.