Chair bondage refers to a bondage position in which a person is tied to a chair. This position is typical of early bondage images which featured damsel-in-distress scenarios (think Bettie Page).
To assume this position, you just need a sturdy chair and some bindings. One person sits in the chair and is then bound to it. There are a number of ways this position can be customized to allow comfort, or to make it less comfortable, depending on the experience you’re looking for.