A gang was a group of associated individuals, often criminals.
The Tenth Doctor briefly considered using the term to collectively address Rose Tyler and Mickey Smith. (TV: School Reunion)
The Thirteenth Doctor sometimes called her group of friends "gang", (TV: The Woman Who Fell to Earth, Rosa, COMIC: A New Beginning, Kerblam!, The Witchfinders, Resolution) as well as "fam" (TV: The Woman Who Fell to Earth, Arachnids in the UK, The Witchfinders, The Battle of Ranskoor Av Kolos, Resolution) and "Team TARDIS". (TV: Arachnids in the UK)
Jack Chance was the leader of Sabalom Glitz's gang of robbers. (PROSE: Mission: Impractical)
The Seventh Doctor was caught in a gang war's crossfire in San Francisco on 30 December 1999. This lead to him regenerating into his eighth incarnation. (TV: Doctor Who)
Baz Bailey was the leader of a gang at Coal Hill School that dealt in illicit drugs. (PROSE: The Eight Doctors)
Elric's father was a judge who crusaded against interplanetary gangs. This made him and his family targets for retaliation; notably, his wife was attacked and left with significant injuries, and Elric was nearly kidnapped from a viewing platform above the planet Cerberin. Jable Rake, a former gang member living alone on Cerberin, was desperate to atone for what he had done. He proved this by helping Elric and Lucie Miller, who had both escaped to the surface, to a radio beacon where Lucie could call the Eighth Doctor for help. (AUDIO: Flashpoint)
Sunset Strip, a market visited frequently by criminal gang members, was most busy on Tuesdays. Rose Tyler described the planet it was on as a "planet of gangsters" (COMIC: Gangster's Paradise)
Near the end of his adventures with Amy Pond and Rory Williams, the Eleventh Doctor traveled with what he excitedly called a "gang." On an trip to a Silurian ark hijacked by Solomon so he could steal and sell its dinosaurs, the Doctor's gang consisted of the Ponds, Queen Nefertiti, and John Riddell, a game hunter from Earth in the early 20th century. (TV: Dinosaurs on a Spaceship)
Abby McPhail and Shawna Thompson wondered if "the Doctor" was a gang leader. (AUDIO: SOS)