"Gender identity can be ambiguous or outside our simplistic understanding of male versus female," explains Walter Bockting, PhD, clinical psychologist and co-director of the LGBT Health Initiative at Columbia University Medical Center. In other words, it's complicated. "Transgender" is an umbrella term that covers a spectrum of people with nonconforming gender identities and expression. Researchers estimate transgender prevalence is 0.5 percent of the population (American Journal of Public Health, 2012).

Clinically speaking, a person who was assigned female at birth but identifies and lives as a man is referred to as a transsexual man, or transman, or female-to-male (FTM); a male-to-female (MTF) person is a transsexual woman or transwoman. Some people drop the trans label after they have transitioned to their new gender, however, and want to be referred to only as a man or a woman.

Cross-dressers are another group under the transgender umbrella. They are usually comfortable with their assigned sex and do not seek to change it. "Genderqueer" is a term used by some in the community who simply describe themselves as falling outside the constructs of male or female. Being transgender may also include those who consider themselves androgynous or multigendered.

Pronouns can become a touchy issue after someone undergoes a transition — social, hormonal or surgical. Use whatever name and gender pronoun the person prefers, most transgender people say, and ask — politely — if you are in doubt. Sometimes the preferred reference may include the descriptor of gay. (For example, a female who has transitioned to male and is attracted to men might identify as a gay man.) But don't confuse gender identity with sexual orientation; they are not the same. Transgender people can be straight, lesbian, gay, bisexual or asexual.

—Eve Glicksman