VU: Unit used for measuring the magnitude of a complex electrical signal.
Originally, an audio output meter for broadcast and recording studio consoles with precisely defined reference level and ballistic characteristics. "VU meter" has become the common name for any audio output metering, particularly on mixers and related equipment.
[link=http://www.google.com/search?num=20&hl=en&lr=&safe=off&rls=GGLR,GGLR:2005-45,GGLR:en&oi=definer&q=define:vu+meter&defl=en]I just googled it and come across these results[/link] but if you can also check at [link=http://en.wikipedia.org/wiki/VU_meter]Wikipedia[/link] as well~!