Here's a breakdown:

* Star: A massive, luminous ball of plasma that emits light and heat as a result of nuclear fusion occurring within its core.

* Planet: A celestial body that orbits a star, is massive enough to be rounded by its own gravity, and has cleared its neighborhood of other objects.

* Star system: A group of planets, moons, asteroids, and other objects that orbit a central star.

Our own solar system is an example of a star system, with the Sun as the central star and eight planets orbiting it.