Trans is an umbrella term for an identity movement. Some of the adherents believe they are they opposite 'gender', despite their sex, for which some feel they need to adjust their bodies via medical and surgical intervention, some don't.
A growing amount of adherents of these beliefs believe they are neither man or woman. Some of them have similar physical interventions, some don't, as before.
Of course, if you ask what they mean by man, woman, male or female, or neither, you will be told that sex and/or gender is a malleable thing, completely arbitrary and adjustable and indefined in either biology or cultural definitions.
There are extremes of this, but from what I can tell, most Enbies (non binary) females are trying to side step sexist and often homophobic constrictions. It's sort of like feminism but a supremely individualistic version. Liberal feminism 2.0.