Multicam is when you use different cameras to record the same thing happening. Let's say you have a birthday party and you want to film it. You might have one camera set up to record the cake being lit up with candles, another camera set up to record the people singing "Happy Birthday," and another camera set up to record your friend blowing out the candles.
After the party is over, you take all of the footage from the different cameras and put them together to make one video. This way, you can see different angles of the same thing happening all at once! It's like having eyes and ears in many different places all at the same time.
Multicam is used in lots of different things like TV shows, concerts, and even sports games. It helps viewers have a better understanding of what's going on by showing different angles and perspectives.