Jómsborg's name is composed of two elements: the Old Norse term borg, meaning a 'fortification'/'stronghold', and the unidentified term, Jóm. The Jómsvikings were an order of Viking mercenaries or conquerors of the 10th and 11th centuries. Though reputed to be staunchly dedicated to the worship of the Old Norse gods, they would also fight for any lord who could pay their substantial fees, even if they may be Christian. The institution of the Jómsvikings would itself foreshadow those of the later religious and chivalric orders of the Middle Ages. The Jómsvikings were highly disciplined, with the organisation being a brotherhood.

The legend of the Jómsvikings appears in some of the Icelandic sagas from the 12th and 13th centuries. According to the sagas their stronghold of Jómsborg was located on the southern shore of the Baltic Sea, but its exact location has been disputed by modern historians and archaeologists.