The Metagame is the 'Galaxy', similar to Total Annihilation's Boneyards. Matches between players take place on planets within a solar system. You do not fight across the galaxy in real time, it is merely a construct that links games together.
Right now there are no galaxies in game, only star systems (which have 1 star and some planets/moons/asteroids). If you're asking this because of the Galatic War feature, see Nanolathe's post above (darn ninja's)
It takes place across multiple systems, but you still fight in a single system at a time. Still a ton of space, though!