Definition of "Mob"

The Mafia: any particular mafia, mentioned uniquely within the discussion's established or implicit context, usually and especially the Sicilian–Italian–Italian-American one (especially in American English) but occasionally others (e.g., the Russian one, the Japanese one).  examples

The masses, especially the 'great unwashed masses': the general population, or (yet more specifically) the rabble thereof, viewed as one mob of unruly, disorganized people predisposed to violence and malevolence.  examples