What is mob? n. 1. A large disorderly crowd or throng. See Synonyms at crowd1. 2. The mass of common people; the populace. 3. Informal a. An organized gang of criminals; a crime syndicate. b. often Mob Organized crime. Often used with the: a murder suspect with links to the Mob. 4. An indiscriminate or loosely associated group of persons or things: a mob of boats in the harbor. 5. Australian A flock or herd of animals.