A drum major is an officer in the army who is in charge of the drummers in a military band, or who leads the band when they are marching.
[British]
2. countable noun
A drum major is a man who leads a marching band by walking in front of them.
[US]
drum major in British English
noun
the noncommissioned officer, usually of warrant officer's rank, who is appointed to command the corps of drums of a military band and who is in command of both the drums and the band when paraded together
drum major in American English
a person who leads a marching band, keeping time with a baton