A chair is a piece of furniture with a raised surface, commonly used to seat a single person. Chairs are supported most often by four legs and have a back; however, a chair can have three legs or can have a different shape. Chairs are made of a wide variety of materials, ranging from wood to metal to synthetic material, and they may be padded or upholstered in various colors and fabrics, either just on the seat or on the entire chair. Chairs are used in a number of rooms in homes, in schools and offices, and in various other workplaces.

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 upholstery, reclining action, and a fold-out footrest, a recliner. A permanently fixed chair in a train or theater is a seat or, in an airplane, 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.