Another meaning for someone who likes to watch others having sex.
More of a medical term, used to denote someone who gets off watching others. Used more as a Psychiatric term, than being a common use word or phrase.
In 2004, Voyeurism without consent was made a criminal offence in the UK.
Canada enacted a similar law in 2005.
Many nations consider 'voyeurism' to be deviant behaviour, and there are laws specifically dealing with such 'acts'.