The Brief: FWB stands for friends with benefits.
Friends with benefits are friends who also have casual sex together. The idea is that they maintain a friendship and a sexual relationship without developing romantic feelings for each other. A FWB relationship is usually based on hookups and a “no strings attached” attitude. FWB can also be used to describe two people who are casually hooking up but aren’t really friends outside of that. FWB relationships can be tricky because one or more person may catch feels for the other.
Random Trivia/Potential Conspiracy Theory:
Friends With Benefits is a 2011 RomCom starring Justin Timberlake and Mila Kunis. It came out the same year as No Strings Attached, a RomCom starring Natalie Portman and Ashton Kutcher. Both films have the same general premise of two people who try to be FWB. Mila Kunis and Ashton Kutcher are married IRL.