Femme is a term used in lesbian and gay subculture to describe an LGBT+ person, typically a lesbian or otherwise sapphic woman (or feminine-aligned non-binary person) who presents femininely. Femme people will often dress in feminine clothing, and typically present themselves in a more stereotypical feminine way, such as having long hair, and wearing makeup. Femmes are also commonly thought of as having more "feminine" interests. Femme women can be cisgender or transgender.
Femme is most commonly associated with lesbians, it is also used by other groups in the LGBTQ+ community. This includes queer men and m-spec sapphics.
Other Terms
Some other terms that are typically synonymous with femme include: "lipstick lesbian" and "designer dyke".
High Femme
Someone who is highly feminine, typically putting in a lot of effort into their appearance. They may chose to only date butch partners.
Stone Femme
Stone femme may refer to a femme who is stone, meaning they do not like their genitals sexually touched by their partners. (They may also identify as asexual, or placiosexual.) It may also refer to the femme partner of a stone butch.