If you are not a lesbian in your waking life, but dream that you are a lesbian, then it signifies a union with aspects of yourself. It is symbolic of self-love, self-acceptance, and passion. You are comfortable with your sexuality and femininity. If, in your dream you abhor the notion of lesbianism, then it represents your fears and rejection of aspects of your own sexuality.
If you are a lesbian in your waking life, then the dream is simply a reflection of your own self.