The Q are an omnipotent alien race in the Star Trek Universe that have miraculous (currently unexplained) powers to control space, time and energy. Use this with the [star-trek] tag.
Q refers to both the name of this incredibly advanced trans-dimensional alien race and also to each member of their race.
They live in the Q Continuum (which exists in another dimension) and treat other races (both physical and non-corporeal) with indifference.
They are considered to be omnipotent, immortal and omniscient, though they can be killed or stripped of their powers by other Q.