Definition of gangbang:
(n) :
(vulgar) An act of two or more people having sex with one person who is the focus of the sexual activity.
(n) :
(vulgar) Synonym of gang rape.
(v) :
To participate in a gangbang.
(n) :
(US, slang) An act of a street gang committing crimes as a group, such as attacking random people on the streets.
(v) :
To belong to a gang; to commit criminal acts as part of a gang.