A mob is a big gathering of people, this group may or may not be violent or angry. The mob is an illegal organization of people that commit crimes. To mob is to have a gathering of people push toward something, surrounding it. This group may just be excited but also may have the intent to attack something.
Demob is a verb, mainly used in British English as an abbreviation for demobilize.
Demobilize is a verb that means to discharge or release from service in the military, or to stop a group or organization, like disbanding them.
Demob can also be a noun used as an abbreviation for demobilization, which is simply the noun form of demobilize.
Demob was coined in World War II.
Jamaican officials say a mob of adults descended on a high school hurling rocks and setting a minibus on fire a day after one of its students allegedly killed a classmate away from the campus. [Star Tribune]
The mob-connected plot to break the legs of a deadbeat suburban businessman started at a dingy used car dealership in Melrose Park, federal prosecutors say. [Chicago Tribune]
As soon as the top cop arrived at city airport he was mobbed by these taxi drivers along with other passengers. [The Times of India]
Adding trombone to his repertoire, he spent his national service playing in a military band and on demob went to London to join Tommy Sampson’s 16-piece big band, one of only three in Britain. [Herald Scotland]