Epicene is an adjective to describe sometime that lacks gender distinction. It can also be used as a gender, or as a way to describe a range of genders.
As An Adjective
Epicene as an adjective describes "that which exhibits characteristics of [male and female], yet is neither". It was historically used to describe effeminate behavior in men and, less commonly, unfeminine behavior in women. It was generally used interchangeably with androgynous.
In linguistics, epicene is used to describe a word that has only one form for both the male and female versions of the word. It is not typically used in the context of English, where there is no grammatical gender, but in languages where nouns have gender by default, an epicene word is considered abnormal.
Gender neutral neopronouns are sometimes called epicene pronouns. Epicene is also occasionally used to describe bisexual or pansexual attraction.
As A Gender
Epicene can be used to describe a non-binary gender that is neutral across masculinity and femininity. However, there is little consensus on a definition so it can sometimes be used to describe any non-binary genders.
Epicene vs. Gender Neutral vs. Androgyne
Epicene is often used interchangeably with either gender neutral or androgynous. Generally the difference is 1) Androgyny describes a combination of masculinity and femininity. Epicenity is neither masculine or feminine. 2) Gender neutrality or neutrois implies a neutrality across all genders. Epicene has neutrality only across masculinity and femininity.