Dominance and submission (also called D/s) is a set of behaviors, customs, and rituals involving the submission of one person to another in an erotic episode or lifestyle. It is a subset of BDSM. Physical contact is not necessary, and D/s can be conducted anonymously over the telephone, email, or other messaging systems. In other cases, it can be intensely physical, sometimes crossing into sadomasochism. In D/s, both parties take pleasure or erotic enjoyment from either dominating or being dominated. Those who take the superior position are called “dominants”—Doms (male) or Dommes (female)—while those who take the subordinate position are called “submissive”—or subs (male or female). A switch is an individual who plays either role. Two switches together may negotiate and exchange roles several times in a session. The term dominatrix usually refers to a female sex worker who dominates others for pay.