A gang bang is a situation in which a person engages in consensual sex acts with several individuals at the same time. Normally there is a single individual who is the central focus of the sexual activity, e.g. one woman surrounded by several men. Rather than serial couplings by two people, the gang bang is defined by the number and simultaneity of the various sex acts such as oral sex, anal sex or double penetration.
Gang bangs are not defined by the precise number of participants but usually involve more than three people and may involve a dozen or more. When the gang bang is organized specifically to culminate with the (near) simultaneous or rapid serial ejaculations of all male participants on the woman (or central man), then it may be referred to by the Japanese term Bukkake.
By contrast, three people engaged in sex is normally referred to as a threesome, and four people are normally referred to as a foursome. Gang bangs also differ from group sex, such as threesomes and foursomes, in that most (if not all) sexual acts are centered on or performed with just the central person. Although the participants of a gang bang may know each other, the spontaneity and anonymity of participants is often part of the attraction. Additionally the other participants normally do not engage in sex acts with each other, but may stand nearby and masturbate while waiting for an opportunity to engage in sex.