Someone who loves guys and girls. Not a confused hetrosexual and not a confused homosexual. Not sex hungry.
Have to prove they aren't more likely to cheat on their partner with someone else just because they are attracted to the same sex.

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.

someone who is atracted to both male and female

The master race.

loving both genders

A person of any gender who has the potential to be attracted to both males and females. This does not mean that they are:

1) trying to attract attention

2) not-quite out of the closet as gay/lesbian

3) confused

4) about to be unfaithful in any way.

A bisexual person has the potential to be attracted to either gender. This doesn't mean that they will be incomplete without regular sex with both genders; it's more of a potential energy thing rather than kinetic. It's also an emotional/romantic thing, not just about sex.

Although some members of the gay/lesbian community look down upon bisexuals, it's just as real and valid as any other sexual orientation.