Transgender people experience a mismatch between their gender identity or gender expression and their assigned sex. Transgender is also an umbrella term because, in addition to including trans men and trans women whose binary gender identity is the opposite of their assigned sex , it may include genderqueer people . Other definitions include third-gender people as transgender or conceptualize transgender people as a third gender, and infrequently the term is defined very broadly to include cross-dressers.
Many transgender people experience a period of identity development that includes gaining better understanding their self-image, self-reflection, and self-expression. The degree to which individuals feel genuine, authentic, and comfortable within their external appearance and accept their genuine identity is referred to as transgender congruence. Being transgender is independent of sexual orientation; transgender people may identify as heterosexual, homosexual, bisexual, asexual, etc., or may consider conventional sexual orientation labels inadequate or inapplicable.
One effort to quantify the population gave a rough estimate that 0.3 percent of adults in the US are transgender, overlapping to an unknown degree with the estimated 3.5 percent of US adults who identify as LGB.
(source : wikipedia)