Imagine drawing a big circle and filling it with tiny stars. The circle of stars is just that - a circle full of stars!
Now, let's imagine we're talking about the circle of stars on a flag - because that's where we usually see them. Have you ever seen the flag of the United States? The flag has a big blue square in the top left corner, and inside that square is a circle of stars.
The stars represent the states in the United States - there are currently 50 states, so there are 50 stars. Each star stands for one of those states.
But the circle itself has an interesting history too. You see, the circle with stars was not always part of the US flag. In fact, the first flag only had 13 stars, for the original 13 colonies. As the US added more states, they added more stars to the flag. But they didn't always know how to arrange them!
At first, they just put the stars in rows or lines. But eventually, someone realized that if they made a circle, it would look much nicer. The circle was first used in the 1800s, and today it is still used on the flag of the US.
So that's the circle of stars - just a pretty way to show all the states on the US flag!