Someone who is in all ways attracted to both guys and girls. It is not because they are sex fanatics, or simply can't decide. Being bisexual is not a phase from people who haven't fully come out yet. It is as real as being straight or gay. You might have a preference over one sex, but bisexual means you can be attracted to both genders sexually, physically, and emotionally. In other words, you are fully capable of FALLING IN LOVE with them, just as a woman would fall in love with a man. It's not a circus freak thing.
Sally fucked Jack and Jill, and enjoyed them both.