Discipline (BDSM)

Discipline is the use of rules and punishment to control overt behavior in BDSM.

Punishment can be pain caused physically (such as caning), humiliation caused psychologically (such as a public flagellation) or loss of freedom caused physically (such as chaining the controlee to the foot of a bed, for some misbehavior). Note the issue of legal consent which may or may not represent a defence to criminal liability for any injuries caused. Practices such as ageplay is an example of discipline in BDSM.

Bondage versus discipline
Bondage when used as a punishment is still bondage, but because it is overtly being done in response to a 'rule' being broken, it is also part of the discipline. Punishment does not need to be physical. It can be loss of privileges, being ordered to do a task (such as writing lines on a blackboard) on threat of further punishment if not finished correctly, it can be verbal humiliation or really any act that can be inflicted on the controlee or get them to inflict on themselves that they don't like.

Rules
Rules can be applied randomly by dominants as a tool for disorienting a submissive. A sadist may also use them as a pretext for punishment. A disciplinarian, on the other hand, is one who enjoys gaining control over someone's physical actions and apparent behaviour by training them to obey stated rules.