One who is attracted to both sexes.
This most certainly does NOT mean that they are all total whores who sleep with everyone that they see.
Both guys and girls can be bisexual.
Bi guys are not: Really gay just trying to be normal
Bi girls are not: Just saying their bi to get in a guys pants.
I do understand that the above things CAN happen, but you should not assume that every bi person fits into one of those catagories.
Samantha found that she was attracted to girls, thus being bisexual, but she still continued to date her boyfriend. They got married and had two kids.
Jeff started dating Sara, but he found that along with the fact that he liked Dave he was getting mild sexual feelings for him too. He decided that he was bisexual. Eventually, he broke up with Sara and asked Dave out, who turned him down. They are still friends.