BDSM is a variety of often erotic practices or roleplaying involving bondage, discipline, dominance and submission, sadomasochism, and other related interpersonal dynamics. Given the wide range of practices, some of which may be engaged in by people who do not consider themselves to be practising BDSM, inclusion in the BDSM community or subculture often is said to depend on self-identification and shared experience.

The initialism BDSM is first recorded in a Usenet post from 1991, and is interpreted as a combination of the abbreviations B/D (Bondage and Discipline), D/s (Dominance and submission), and S/M (Sadism and Masochism). BDSM is now used as a catch-all phrase covering a wide range of activities, forms of interpersonal relationships, and distinct subcultures. BDSM communities generally welcome anyone with a non-normative streak who identifies with the community; this may include cross-dressers, body modification enthusiasts, animal roleplayers, rubber fetishists, and others.

Activities and relationships in BDSM are often characterized by the participants' taking on roles that are complementary and involve inequality of power; thus, the idea of informed consent of both the partners is essential. The terms submissive and dominant are often used to distinguish these roles: the dominant partner ("dom") takes psychological control over the submissive ("sub"). The terms top and bottom are also used; the top is the instigator of an action while the bottom is the receiver of the action. The two sets of terms are subtly different: for example, someone may choose to act as bottom to another person, for example, by being whipped, purely recreationally, without any implication of being psychologically dominated, and submissives may be ordered to massage their dominant partners. Although the bottom carries out the action and the top receives it, they have not necessarily switched roles.

The abbreviations sub and dom are frequently used instead of submissive and dominant. Sometimes the female-specific terms mistress, domme, and dominatrix are used to describe a dominant woman, instead of the sometimes gender-neutral term dom. Individuals who change between top/dominant and bottom/submissive roles—whether from relationship to relationship or within a given relationship—are called switches. The precise definition of roles and self-identification is a common subject of debate among BDSM participants.