Chair

A chair is a piece of furniture for sitting, consisting of a seat, a back, and sometimes arm rests, generally for use by one person. Chairs also often have four legs to support the sit raised above the floor. Without back and limb rests it is called a stool. A chair for more than one human being is a couch, sofa, settee, loveseat, recliner or bench. A split footrest for a chair is known as an ottoman, hassock or poof. A chair mounted in a vehicle or in the stage is simply called a seat. The back often does not expand all the way to the seat to allow for ventilation. Likewise, the back and sometimes the seat are made of permeable materials or have holes drilled in them for decoration and ventilation.
The back may extend above the stature of the head. Headrests for seats in vehicles are important for prevent whiplash injuries to the neck when the vehicle is occupied in a rear-end collision.
Chair design considers planned usage, ergonomics, as well as non-ergonomic functional requirements such as size, stack ability, fold ability, weight, durability, stain confrontation and artistic design.