Effeminacy describes traits in a human male, that are more often associated with traditional feminine nature, behaviour, mannerisms, style or gender roles rather than masculine nature, behaviour, mannerisms, style or roles.

It is a term frequently applied to womanly behavior, demeanor, style and appearance displayed by a male, typically used implying criticism or ridicule of this behaviour (as opposed to, for example, merely describing a male as feminine, which is non-judgmental). The term effeminate is most often used by people who subscribe to the conventional view that males should conform to traditional masculine traits and behaviours. Generally, the description is applied to individuals, but may be used to describe entire societies as an inflammatory allegation. Although in the Western tradition, as described below, effeminacy has often been considered a vice, indicative of other negative character traits and often involving a pejorative insinuation of homosexual tendencies, in other societies, feminine males may be considered a distinct human gender (third gender), and may have a special social function, as is the case of Two-Spirits in some Native American groups. Furthermore, in contemporary culture, effeminacy has come to be seen by some to be simply one characteristic or trait which might be a part of a particular person's "gender role", and in this sense would not be considered a vice or indicative of any other characteristics. An effeminate male is similar to a fop or a dandy, though these tend to be archaic identities that are taken on by the individual rather than insulting labels.