Discipline in BDSM refers to the practice where the dominant sets rules for the submissive that he/she is expected to obey. When rules of expected behaviour are broken, punishment is often used as a means of disciplining.
In BDSM, rules can be made so that a submissive ("sub") knows how he/she should behave (so that the dominant is not displeased). Rules can also be for reminding subs of their inferior status, or for training a novice sub. When such rules are broken, punishment is often used as a means of discipline. Punishment itself can be physical (such as caning) or psychological (such as public humiliation) or a combination of both (i.e., through bondage).
The goal of discipline is to teach the sub that he/she has made a mistake, so that he/she learns self-restraint and becomes a better sub in the future. The punishment is generally related to the mistake, and is generally proportionate to the severity and frequency of the mistake. For example, a punishment for speaking out of turn for the first time may be a simple restraint (such as being silenced using a gag). The sub may also be given the option of choosing a punishment (i.e., to be either caned on the buttocks or slapped on the face).
Punishments done on BDSM submissives, even very harsh ones, should not be confused with sadomasochism. S&M involves giving pain to a "sub" for the enjoyment of at least one person. Contrarily, punishments for disciplining are in response to violations of predetermined rules by a sub, or for otherwise displeasing the dominant. Punishment is a necessary evil in BDSM, as without it, a sub may repeat mistakes and thus not improve as a sub. Punishment is also not forced abuse – in the former a sub must have granted the trainer prior authority to punish. Punishment should also not be confused with BDSM training which may involve giving pain just for increasing the endurance limit of the sub.
Sometimes, disciplining may avoid punishment altogether, and just a hard glance or loud voice from the dominant may be effective.
Contrary to punishments, which are negative reinforcement, disciplining may also involve positive reinforcement. This includes rewarding the slave (such as by praising) for good behaviour. 
- Bound and Shagged: Discipline, Swarthmore College Daily, Oct 2012, retrieved 27 Aug 2017
- Encyclopedia of Social Deviance, page 75, SAGE Publications, 2017 ISBN 9781483364698
- Bill Henkin, Sybil Holiday: Consensual Sadomasochism: How to Talk About It and How to Do It Safely, Page 71. Daedalus Publishing Company, 1996, ISBN 978-1-881943-12-9.
- What is BDSM?, MensXP, October 2015, retrieved 27 August 2017