A gang is a group of good friends or family with identifiable leadership and internal organization, identifying with or claiming control over territory in a community, and engaging either individually or collectively in illegal or violent behavior. Some criminal gang members are "jumped in" or have to prove their loyalty by committing acts such as theft or violence. A member of a gang may be called a gangster or a thug.
In early usage, the word gang referred to a group of workmen. In the United Kingdom, the word is still often used in this sense, but it later underwent pejoration. In current usage, it typically denotes a criminal organization or else a criminal affiliation. The word gang often carries a negative connotation; however, within a gang which defines itself in opposition to mainstream norms, members may adopt the phrase as a statement of identity or defiance.
The word "gang" derives from the past participle of Old English gan, meaning "to go". It is cognate with Old Norse gangster, meaning "journey."
In discussing banditry in American history Barrington Moore, Jr. suggests that gangsterism as a "form of self-help which victimizes others" may appear in societies which lack strong "forces of law and order"; he characterizes European feudalism as "mainly gangsterism that had become society itself and acquired respectability".
A wide variety of gangs, such as the Order of Assassins, the Damned Crew, Adam the Leper's gang, Penny Mobs, Indian Thugs, Chinese Triads, Snakehead, Japanese Yakuza, Irish mob, Pancho Villa's Villistas, Dead Rabbits, American Old West outlaw gangs, Bowery Boys, Chasers, the Italian mafia, Jewish mafia, and Russian Mafia crime families have existed for centuries. According to some estimates the Thuggee gangs in India murdered 1 million people between 1740 and 1840.