Refers to who you are attracted to (sexual orientation). T (Transgender): Refers to who you are (gender identity).
Despite this foundational role, trans people have historically faced marginalization even within the gay and lesbian rights movements. In the 1970s and 80s, some feminist and lesbian groups excluded trans women, viewing them as "men infiltrating women’s spaces." Similarly, the mainstream gay rights movement sometimes sidelined trans issues to appear more "palatable" to cisgender (non-trans) society. This painful history gave rise to the phrase —a rejection that trans activists have fought against, insisting on unity.
Understanding these terms is key to respectful engagement with the community.