Boss was a title on Sigma Iotia II. A boss was the head of an outfit, through which he administered territory. The title was originated from 20th century Earth history, as the Iotian culture was patterned on the book Chicago Mobs of the Twenties, which made its way to the planet in the mid-22nd century.
Bosses and their outfits operated in lieu of conventional government: people were expected to pay "a percentage" in return for which the boss would take care of their needs. In 2268, there were "maybe a dozen" bosses on the planet, not counting small fry. (TOS: "A Piece of the Action")