A player is a person who actively participates in BDSM activities. Fans of rope bondage, sadists, masochists, and people who simply enjoy kinky sex may all consider themselves players. Players are the participants in BDSM scenes, just as the players in the theater play in scenes.
A player is sometimes called a practitioner.
An alternative meaning to the term is someone who keeps lot of other people interested in them for relationships, but is not committed to just one person.