Femme is a term used in lesbian and gay subculture to describe a lesbian, bisexual, or otherwise sapphic woman (or feminine-aligned nonbinary person) who presents femininely. Femme women and enbies 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, however any women or fem-aligned enby who is attracted to women can identify as femme, including bisexual women, pansexual women, etc. Non-wlw members of the LGBT+ community also use the femme label too.
Other Terms
Lipstick lesbians is typically synonymous with femme. There is an emerging usage of the term high femme, which indicts someone who is highly feminine, typically putting in a lot of effort into their appearance.