A big band is like a big group of musicians playing music together, kind of like a really big orchestra. But it's a special kind of group that plays jazz music, which is a fun and lively type of music. The big band usually has a lot of people playing instruments like the saxophone, trumpet, trombone, and drums. They all work together to make the music sound really cool and make people want to dance. You might have heard big band music in movies or on TV shows from a long time ago, but some people still love listening to it today because it's just so much fun!