Gender expression/presentation is a person's behavior, mannerisms, interests, and appearance that are associated with gender in a particular cultural context, specifically with the categories of femininity or masculinity. This also includes gender roles. These categories rely on stereotypes about gender.
Gender expression refers to people’s manifestation of their identity to others, though, for instance, dress, speech, and mannerisms. People’s gender expression may or may not match their gender identity/identities, or the gender/sex they were assigned at birth. These are the different ways people express their gender identity and perform it socially. It can be fairly feminine, more masculine, more androgynous... We are talking about ways to dress, walk and move, to wear or not makeup, talk, wear this or that physical attribute (such as hairstyle, body hair, etc.).
The expression of gender varies enormously according to the regions of the world and the period. Gender expression should not be confused with gender identity. For example, it is quite possible to identify oneself as a man (gender identity) and to have a somewhat "feminine" appearance (gender expression), for example, by wearing so-called "feminine" clothes or even makeup.