In contemporary kink, a Master is a person who consensually takes ownership over someone who they are in a relationship with.

This Role In Core BDSM

In core (or traditional) BDSM, Master is not a role, but a title for a specific form of Dominant and pertains to BDSM only. A Master accepts (or has accepted) absolute total authority and assumes ownership of a slave. A Master is someone who "owns" a submissive as property — an indication that another human being found them trustable and experienced enough to transfer their whole agency to them.

A Master accepts responsibility and accountability for the totality of another human being’s life (very different from real life human trafficking / slavery).

It is expected that a Master possess advanced and correct knowledge of BDSM. The title is not usually self-given, but is an honor bestowed on someone as an acknowledgement of their competency by other experienced practitioners of core BDSM. It can sometimes take decades to reach the level of competence needed to earn the title of Master. Being given the title means they have experience, knowledge, and understanding of the lifestyle and of what these roles require. This includes demonstrating core values as well as being skilled at the things they use as toys. Often this title comes with responsibilities such as handing down BDSM knowledge to newer practitioners.

For a core BDSM Master/slave dynamic, consent is given to the negotiated dynamic rather than to individual actions. The dynamic is recognized as a total power exchange, so consent is considered to be irrevocable after negotiation. If consent is revoked or changed, then the dynamic is often considered broken — similar to a marriage ending in divorce. Safe words are therefore usually only used as emergency stops instead of a withdrawal of consent.