Define a chair.

[Muffin]

Anything that you can sit in comfortably without it breaking or leaving marks (a.k.a Damage) the object.

[Ad Bot]

[_Rave_]

A chair is a stable, raised surface used to sit on, commonly for use by one person

As defined by Wikipedia.

[GodlyFireFight]

A chair is a physical object with its own energy and mass which can hold your weight while you sit on it. It can be supported by curved boards, four poles, or a box of which can be sat on.