Complex sentence: Crooner is an American epithet given to male singers of pop standards, mostly from the Great American Songbook, from the 1920s to the 1950s and normally backed by a full orchestra or big band.
Split into simpler sentences: Crooner is an American epithet given to a male singer of 1920s to 1950s pop standards, mostly from the Great American Songbook. He is normally backed by a full orchestra or big band.