The definitions according to American Heritage Dictionary:
Gay - A person whose sexual orientation is to persons of the same sex. (Homosexual)
Lesbian - A woman whose sexual orientation is to another woman.
Bisexual - Of, relating to, or having a sexual orientation to persons of either sex.
Transgendered - Appearing as, wishing to be, or undergone surgery to be a member of the opposite
sex.
GLBT - Gay, lesbian, bisexual, transgendered community.