its the same as a regular monitor for guitar or whatever....if youre playing in bigger shower, the vocalist wont necessarily be able to hear himself sing because of all of the volume/noise around him (amps, drum, crowd, etc). It basically just runs a feed to his/her ear so they can hear themselves.
anyone know a song that like has lyrics like that i promised you i promised you blown away blown awaya yea i like that i like that ARGGHGHGHGHGHGH ??? am looking for it like 1 month now