I'm attempting to not go into lecture mode. There are two forms of asexuality when it comes to humans. One, is where the subject does not have any sex drive or does not want to attempt copulation, regardless of partner. The other kind, is where they simply do not have any preference. I fall into the middle: I don't care what gender they are, but I don't really want to 'do it' anyway. Bisexuals specifically like both genders to varying degrees, and pansexuals.. are even harder to describe.
But again, this is off topic and approaching a grey area.
Edit: Not wanting to bump the thread further with offtopicness, ExHunterEmerald has a point. Tonight was a rough night for me, and I was unnessicarially harsh. Asexual is the term my therapist uses.