Femininity

Femininity is the traditional set of archetypes associated with women and girls. Femininity by its very nature is a social construction, but is based off of a mixture of cultural and biological components. This makes it distinct from the biological "female" sex, as both men and women can display so-called "feminine" features.

Stereotypes
Femininity is traditionally associated with traits such as empathy, compassion, and humility. While by itself femininity isn't a bad thing, the negative stereotypes that pop up with femininity include that feminine people are supposedly more submissive than so-called "masculine" people, and the traditional ideal of "femininity" has been associated with the oppressive role of the "house wife," and so feminine people are often culturally coerced to take jobs as, say, secretaries and teachers, if they are to be allowed jobs at all that is according to cultural norms. "Stay in the kitchen" is still very much in effect sadly.

Women are often less valued as leaders, because people view femininity as not being a "leadership quality." The harmful cultural attitudes against femininity also contribute to gender inequality.

In short
You don't have to be a woman to be feminine, and the reverse is also true. There are femme boys, femme enbies, and femme genderqueer people. Gender itself is a spook, and a fundamental part of queer liberation is rejecting the shackles of societal expectations and norms about gender.