Minecraft wiki entry for music, associated text: Specifies a music track to play.
Must be a string. Must be either a single word (no spaces) or a quoted string.
Must be a music track name (e.g. record.cat), or a music track defined under the Json path "record.<music_name>" or "music.game.<music_name>" in the <a_resource_pack>/sounds/sound_definitions.json file (e.g. cat to play "Cat" music disc).