Quite a few games and settings (I've done it myself) occur within concentrations of habitable systems, maybe a few dozen or a few hundred, of definite extent and situated some distance away from the main expanse of the galaxy, often but not always with a name.
In some ways, this might just be an equivalent of the fantasy continent-on-a-page map - to put it most harshly, a failure of imagination - but they seem to have some useful qualities. Maybe we can say some things in general about them from actual observations (say, of moving groups
and open clusters
) or as a convention.
It might also help to distinguish stellar groups that are not as useful for the space opera style of gaming. Globular clusters
, for instance, are probably too dense, too elderly and too far from the galactic disk to offer a familiar setting.