From Astro Wars
A Star System is a place usually composed of 12 planets (it can be less while players are creating their accounts and arriving in that system). It has coordinates, and the planets are numbered from 1 to 12.
Each Star System is frequently evaluated for size and activity of that Star System. Evaluation involves taking the average of the lowest and the highest level of Population in the planets in the System, including Free Planets (which consequently have a population of 0).
Results are displayed on your map and on the Star map when you click on the Location link in a player's profile.