Gender expression is how an individual chooses to express themselves. The societal norms dictates gender expression to be binary in terms of feminine traits and masculine traits. However, in reality there is no feminine or masculine, there are just expression that an individual chooses. Some of the ways an individual can choose express their gender is by their pronouns, hairstyle, the way they dress, body language, among others.
Sources:
https://www.hrc.org/resources/sexual-orientation-and-gender-identity-terminology-and-definitions