Billions of stars in the same region of the universe are called a galaxy.

Here's a breakdown:

* Galaxy: A massive, gravitationally bound system consisting of stars, stellar remnants, interstellar gas and dust, and dark matter. Our own galaxy is called the Milky Way.

* Stars: Massive, luminous spheres of plasma held together by their own gravity. They emit light and heat as a result of nuclear fusion reactions in their core.

So, while a galaxy is a vast collection of stars, stars themselves are the individual building blocks of a galaxy.