Have you ever watched a movie or played a video game and heard a loud explosion, a gunshot, or a big crash? Well, sometimes those sounds aren't recorded in real life, they're actually made by people who specialize in creating sounds for movies, TV shows, video games, and more.
Those people are called sound designers, and they use things like drums, synthesizers, and even vegetables to make all sorts of different noises. Some sound designers even record real sounds and then use computers to make them sound even cooler.
Now, sometimes those sound designers make sounds that are so good and so useful, that they get put into a big library of sounds called a stock sound effect library. These libraries have TONS of different sounds, from animals to car crashes to explosions to silly cartoon noises.
When filmmakers or video game designers need a certain sound for their project, they can search through the stock sound effect library and find the perfect one. It's kind of like going to a big toy store and picking out exactly what you want.
So next time you hear a sound in a movie or video game, just remember that it might have come from a big library of sounds that sound designers made.