Quote Originally Posted by Subterranean
'the Sun is large, round and yellow, if not large, round and yellow, it not Sun'
The Sun belongs to a group called stars. Though the Sun is yellow, all stars are not. Stars also differ in size, but they are all rather large. Stars tend to be round, too, but due to gravitation and/or centrifugal force, a star may be not perfectly circular in some circumstances.

Definition: Star is a concentration of plasma, held together by gravitation. In some part of the evolution of a star there is nuclear fusion in it.

/* There might be some mixed in this explanation, I'm sorry for that. */