What is the universe?
Everything. The universe is all matter and all space; the cosmos.
There is one confirmed universe. This universe is believed to be around 10 billion lightyears across (lightyear is a unit of measurement used to measure cosmic distance. In example, it takes light 2.5 million years(lightyears) to reach the Andromeda Galaxy).
Within this universe of expanding space is matter, which is everything physical. There are an estimated 100 billion galaxies in the observable universe.
Earch galaxy is different sizes, but in our galaxy, the Milky Way Galaxy, there are around 300 billion stars. And let's say if 10% of the stars have orbiting planets, there are about 30 billion planets in our galaxy.
All of which, and many more make up the universe