From "The Gay Slang Dictionary"
1. [kwn LV, mid 60s] to date woman to prevent the suspicion of being homosexual.
2. a woman who dates a homosexual to prevent suspicion of his homosexuality, or to help him socially. Synonyms: flinking
3. n. a straight woman married to or involved with a gay man. The gay man may be in the public eye, and may have a beard to hide the fact that he is gay. ("She is just his beard.")