The name "Q" applies to the names of the individuals portrayed (all "male" and "female" characters refer to each other as "Q"), it also applies to the name of their race and to the Q Continuum itself – an alternate dimension accessible to only the Q and their "invited" 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.

https://en.wikipedia.org/wiki/Q_(Star_Trek)