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.
Q's second appearance was later in the first season, in the episode "Hide and Q", when he decides to admit a human into the Continuum. Q believes that humanity has the potential to one day evolve beyond the Q, and he wants to understand how. He settles on Picard's first officer, Commander Riker, but Q fails to trigger the evolution and Riker remains human. Thereby losing a wager with Picard, Q is bound by the terms of the wager to stay out of humanity's path forever. Q instantly vanishes, but continues to appear in later episodes as if the wager never occurred.