A jazz band is a special group of musicians who play jazz music together. In a jazz band, there isn't a conductor like you might see in an orchestra. Instead, one of the musicians takes the lead. This person is often called the 'band leader' or 'soloist'. They help the others know what to play and when, but everyone can share their own sounds too!
Think of it like playing on a playground. Everyone has their own game, but one person might suggest a fun game for everyone to play. In a jazz band, all the musicians get to do their own thing while still making beautiful music together!