Bisexual is only the context that most think about. I think of people as being sexual or not. In that, bisexual to me is just those who acknowledge the capability of having sex with both sexes.
I love the term hetro-flexible. I'm basically straight, unless it's the right woman.
Really, though, I think we are all somewhere on the continuum with gay at one end and straight at the other, and very very few people solidly at one end or the other. And sometimes we drift.