What does homosexual, heterosexual, bisexual mean?

These are categories of sexual orientation that can either describe a behavior or an identity. As an identity, some people who are attracted to the opposite sex self-identify as heterosexual, some attracted to the same sex self-identify as homosexual and some attracted to both sexes self-identify as bisexual. Some women who are attracted to other women might label themselves lesbians and some men attracted to other men may label themselves as gay. These categories also refer to behaviors and not identities; you can read more about this in the next question.