A paramilitary was a militarily-structured group that was not part of an official military organization sponsored by the state, comprised of civilians. One notable example was the Maquis.
In 2370, Captain Jean-Luc Picard assured Gul Evek that "Starfleet does not condone the Maquis' actions in the Demilitarized Zone any more than your government would condone the paramilitary actions of Cardassian civilians." (TNG: "Preemptive Strike")