A Master is a male dominant in the BDSM community. Typically, Masters exert ultimate control over their submissives, or slaves, who are submissive members of the community.
Although the terms used to describe these arrangements - Master and slave - make them sound like someone is being forced, this is not the case. The Master/slave dynamic is a consensual agreement in which submissives choose to submit their freedom to their Masters. In return, their Masters are responsible for seeing to all of their slave's needs and are also responsible for their safety. The terms and limits of a Master and slave's relationship may be solidified with a formal contract.
Although the Master/slave dynamic is a form of consensual roleplay or enacted as part of a committed submissive lifestyle, some view the imagery as problematic as a result of the historical context from which it arises.
The female version of a Master is usually referred to as a Mistress.