How is a person who identifies as transgender different from...
A transsexual? The term transsexual usually refers to someone who not only identifies with a gender other than the one he or she was assigned at birth, but wants or has already gone through surgical or hormonal procedures to change his or her sex.
A transvestite? Someone who is a transvestite enjoys dressing in clothing typically worn by the opposite gender but does not wish to live as a member of that gender or feel like he or she was born the wrong sex. Transvestites usually cross-dress for sexual pleasure, not because they identify as a member of the opposite gender.
Being gay or lesbian? Sexual orientation is different from gender identity. A transgender person might be gay or straight, or they might not identify with either label.