Someone in Quora said this about the mafia and cosa nostra:

Cosa Nostra is, essentially, the American descendant of the Sicilian Mafia. The members never referred to their organization as anything but “our thing” or “our business,” and the Italian phrase was eventually adopted by some elements of American law enforcement as the name of the national organization.

As a practical matter, the terms Mafia and Cosa Nostra are used synonymously, along with, “The Syndicate,” “The Organization,” “The Mob,” and (in Dick Tracy) the “The Apparatus.” Subsidiary elements of the nationwide organization include “The Outfit” (for the Chicago branch), “The Five Families” (the various branches in the NYC metropolitan area), “The Mayfield Road Mob” (Cleveland), “The Office” (the Boston/New England branch), “The Detroit Partnership” (the Michigan branch), “The Combination” or “The Combine” (a coalition of all the Eastern Seaboard Mob families), etc.