A video game content rating system is a way to judge and label the content in a video game and what ages it is okay for. It is similar to the movie rating system.
For example, games with violence or drugs might be marked as teen/adult games that might not be okay for children to play. Games with nudity and adult content might be marked as Adult Only, which means that only adults can buy the game and play it.
There are many different game content rating systems all over the world.