A Star System is a collection of stars and planets that inhabit a parsec hex on a sector map. A star system may have zero stars, in which case it will most probably consist of a rogue planet.
An empty system has no stars or planets. Generally these won't be defined in the database.
A single star with zero or more planets. These are the simplest functional star systems.
A binary star system has two stars in orbit around each other. There are several different types of binary star system, depending on the proximity of the stars to each other, and their size relationship.
A conjoined binary consists of two stars that are close enough that their atmospheres are touching. These are quite rare, and can lead to an unstable system due to frequent solar flares of extreme magnitude. Though planets can orbit both stars at a distance, they are unlikely to be able to support life.
Such stars are often asymmetrical, with one being significantly more massive than the other. Some though consist of matched pairs.
A close binary has two stars orbiting within 1 AU of each other. The stars are not touching, but they are close enough that it is possible for planets to orbit both stars. Any planet will tend to be at least ten times the distance between the two stars.
A medium binary has two stars between 1 AU and 100 AU of each other. They are not close enough for planets to orbit both stars, but planets could orbit each star, depending on exactly how far apart they are.
A far binary has both stars significantly far from each other, more than 100 AU. In such cases the other star may not be recognised as a sibling by people on a planet on the first star, at least until they achieve a suitable level of astronomy.
The regions within a solar system are split into zones based on their proximity to the star. This dictates the type of planets that may be present.