Answer:
The answer is "galaxies."
Step-by-step explanation:
The "universe" is also called "the cosmos." It includes space, time and heavenly bodies such as planets, sun, moon, galaxies, etc.
A galaxy is considered to be a big collection of gas, dust, stars (including their solar systems). All of these are being held together by "gravity." The Earth's galaxy is called the "Milky Way." The name is derived from how it appears from afar.
Other than our galaxy, there are millions or even billions of other galaxies in the universe! They come in different colors, shapes and sizes. They appear clustered together due to "mutual gravity." A cluster consists of hundreds to thousands of galaxies.