Hormone therapy

Femme is a term that refers to a queer person whose gender expression is considered to be feminine. It was originally used to distinguish feminine lesbian and bisexual women from butch women, and it is still one of the main uses of the term. It's common for trans and non-binary individuals to use the term to refer to their identity or expression even if they do not identify as lesbian or bisexual women. However, this last usage is a bit controversial.

Difference between femme and feminine
The word femme can only be used to describe people in the LGBTQ+ spectrum. That means that cisgender straight women should not use the term to describe themselves, as it would be considered appropriation. Because there are many stereotypes surrounding femininity, the term femme is often used to subvert cultural expectations about how a woman should look like. For this reason, many (but not all) people that identify as femme do not try to adhere to these stereotypes. This is similar to how the word queer was reclaimed by the LGBTQ community.

Usage within the nonbinary community
Although originally the term femme was used to describe women only, its usage has been expanded to the nonbinary community. It is rarely used as a standalone identity, as it normally describes nonbinary people that have a feminine gender expression. This might lead to difficulties for the femme-identifying individual caused by the false assumption that all nonbinary people have an androgynous expression.

Controversy
The usage of this term by people who do not identify as women is a bit controversial. Some people claim that in the same way that nobody uses the words bear or twink unless they are gay men, nobody should use words such as femme or butch unless they are women. Therefore, they consider it appropriation.