Chair

A chair is a piece of furniture for sitting, consisting of a seat, a back, and sometimes arm rests, usually for use by one person. Chairs also often have legs to support the seat raised above the floor. Without back and arm rests it is called a stool. A chair for more than one person is a couch, sofa, settee, loveseat (two-seater without arm rest in between) or bench. A separate footrest for a chair is known as an ottoman, hassock or poof. A chair mounted in a vehicle or in a theatre is simply called a seat. Chairs as furniture are characteristically not attached to the floor and so can be moved.
The back often does not make bigger all the way to the seat to allow for ventilation. Likewise, the back and sometimes the seat are made of porous materials or have holes drilled in them for decoration and ventilation.
The back may expand above the height of the head. There may be separate headrests. Headrests for seats in vehicles are important for preventing whiplash injuries to the neck when the vehicle is concerned in a rear-end collision.