A word combining "Slay" and "Purr" used when you see something that is slaying, cool, hot, ect! Not to be mistaken for slur as in the offensive/insulting version.
According to the movie "Cyberbu//y", it's an alternative to the word "Slut". Assuming it's only used because the movie was made for T.V. and the word "slut" is far to vulgar for T.V. audiences.