* Universe: The largest of them all. It encompasses everything, including all galaxies, stars, and planets.

* Galaxy: A vast collection of stars, gas, dust, and dark matter held together by gravity. Our galaxy, the Milky Way, is home to our solar system.

* Solar System: A star (our Sun) and all the planets, moons, asteroids, and comets that orbit it.

* Star: A massive, luminous ball of plasma held together by its own gravity.

In summary:

* Universe > Galaxy > Solar System > Star

The Universe is the largest entity we know of.