Came across this Gay Guy With A Beard hilarious urban dictionary expression and what it means. Sometimes folks who are gay but don’t want to step out of the closet or throw off suspicion use another person, a wife, a girlfriend etc., to let others think they aren’t gay. In this case the wife or the girl friend is the beard. Most of the times the ‘beard’ does not realize they are playing the part of the beard. (I would find it hard to believe though, maybe its a relationship of convenience).
Sometimes gay guys like to keep a beard for genuine reason.