friend with benefits; fuck buddy
Casual abbreviation of セックスフレンド. Used among younger speakers to refer to a sexual partner without romantic commitment. Can sound crude or flippant depending on context.
See also: セックスフレンド
Before I knew it, he and I had become friends with benefits.
Those two aren't dating; apparently they're just friends with benefits.
Rather than finding a fuck buddy, I want to look for a real partner.
The two of them are keeping up a friends-with-benefits relationship.
Out of loneliness, she got herself a friend with benefits.
友達 means an ordinary friend with no sexual connotation, while セフレ (from セックスフレンド) specifically implies a sexual relationship, so learners may misread the 'フレ' part as simply meaning 'friend'.
counter for people
Abbreviation of セックスフレンド (sekkusu furendo), from English 'sex friend'. The exact derivation is straightforward; the clipped form emerged in casual Japanese speech.