System
"System" is a term that is flung around willy-nilly in the Star Wars Hexalogy[1]. It is never quite clear from its usage in the movies what is meant by the term, and the hosts and guests have often speculated back and forth as to its the meaning. However, it is an actual term used in astronomy[2][3]. It refers to any body in space around which natural satellites orbit. The Solar system consists of our sun Sol, and all the planets, planetoids, asteroids, and comets that orbit it. The Earth and its moon (Luna) can also be thought of as a system, the Earth-Moon system. This was discussed in ROTJ Minute 105.
References
1. http://en.wikipedia.org/wiki/Hexalogy
2. http://en.wikipedia.org/wiki/Planetary_system
3. http://en.wikipedia.org/wiki/Satellite_system_(astronomy)