Gender dysphoria refers to emotional and social distress experienced by an individual identifying with a gender that is incongruent with their biologic sex characteristics. Biological sex refers to anatomic sex, determined by anatomic sex characteristics. Gender assigned at birth refers to the gender marked on a birth certificate, which is based on a newborn's external genitalia. Transgender or nonbinary gender is characterized by an individual identifying with a gender that is incongruent with their assigned gender at birth. These individuals are at increased risk for gender dysphoria, although gender dysphoria can occur in individuals who identify with their birth-assigned gender.

The abbreviation FTM (female-to-male) is often used in the literature to describe a transgender man's transition. Conversely, MTF (male-to-female) is often used to describe a transgender woman's transition. Gender nonbinary is a broad term that describes many other gender identities that do not conform to the binary male / female construct. Examples include gender nonbinary, gender nonconforming, agender, gender expansive, and genderqueer.

It is difficult to assess the prevalence of gender diversity and gender dysphoria in the population for numerous reasons. The US census and other surveys often have gender options that conform to a binary gender system, limited to only male or female. Many gender-diverse individuals do not seek out medical treatment, so they may not be included in medical records. In some circumstances, it may not be safe for some people to identify themselves publicly as not conforming to their birth-assigned gender. All of these variables make total population estimates of transgender or gender nonbinary individuals inaccurate (likely underestimated), and therefore underestimate the prevalence of gender dysphoria.

Gender dysphoria can also refer to the formal diagnosis listed in the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5); however, not all transgender and gender nonbinary individuals experiencing gender dysphoria meet those criteria. Furthermore, not all gender-diverse individuals experience gender dysphoria.