According to the enotes dictionary, the definition of a system is that it is "A group of interacting, interrelated, or interdependent elements forming a complex whole" The concept of a system is also a group of objects occurring naturally like the planets in our Solar System. All of the planets are dependent on each other and our sun to stay in place. If it were not for the pull of gravity and the interaction between all the planets in our system there could be no seasons, tides, day and night etc. Because all of these objects are directly influencing each other we call it a system. The Sun is the center of our system and Solar is a term used in conjunction with sun.