Androgynous is used sometimes to describe a type of appearance that mixes both masculine and feminine aspects, often such that the person's gender is ambiguous, and they don't clearly read as either male or female. It is also a term that people sometimes use to describe their own gender identity—the way they feel and present themselves in the world. Like any gender identity other than man or woman, androgynous doesn't conform to the binary: some people consider it in the middle of a gender continuum (a harmony or blend of masculine and feminine), and others consider it outside altogether.
While some would say that there's no such thing as a human without any gender, androgynous is sometimes used to describe a way of presenting oneself in public without gender. Some (but by no means all) people who identify as androgynous may reject the gender binary by rejecting gender completely.