Slang for a woman's vagina.
Mistakenly credited to 'Least I Could Do', but actually first showed up in the pages of a Fate/Stay Night doujinshi years before the webcomic used the term.
Since the original doujinshi censored the word "vagina", it showed up as vag followed by several OOOs.
"Here! ......My vagOOO! To my... my..."