Okay kiddo, have you ever seen a cartoon where someone falls and there's a "boing" sound? That's a sound effect!
Sound effects are sounds that don't come from people or music but are added to a movie, TV show, or video game to make it more interesting or realistic.
For example, when you're watching a movie and a character opens a door, you'll probably hear a creaking sound. That's a sound effect to make it seem like the door is old and not very well-maintained.
Sound effects can be made in different ways, like by recording actual sounds in the real world, or by using special machines and computers to create the sounds digitally.
Sometimes sound effects can be funny, like the "boing" sound, and sometimes they can be really scary, like the sound of a monster growling.
So, that's what a sound effect is, it's just a special sound that people add to movies, TV shows, and video games to make them more fun to watch or play!