Q is a being who is unconstrained by, and indeed possesses power over, normal human notions of time, space, and even reality itself – he and his fellow Q are said to be omnipotent, and he is continually evasive regarding his motivations. The name "Q" also applies to all other individuals of the Q Continuum – an alternate dimension accessible to only the Q and their guests. The true nature of the realm is said to be beyond the comprehension of "lesser beings" such as humans, therefore it is shown to humans only in ways they can understand. He is an awesome character and deserves to have some caches hidden in his honor. As an added bonus, this series will place quite a few Q caches in the pool to assist folks with the need.
In "Déjà Q", Q is punished by the Q Continuum by being made mortal; his committing of an uncharacteristically selfless act (sacrificing his life so that a race attacking him won't destroy the Enterprise) garners the return of his powers. In the same episode, Q says that Picard is "the closest thing in this universe that I have to a friend."