Nikubenki is a japanese term(although its a slang) which is often used by 2ch men to describe women who have had sex before, possibly to describe those who have sex with every man(or only with their boyfriends) but not with the 2ch men. the term does not exactly mean "slut" in English. a slut means woman who loves to and has sex very with a lot of men randomly. However Nikubenkis migh not always sleep with a lot of men.