Xenbinary means xenine/xenic binary. Someone who has gender binary but leans xen(sex), is midbinary or endobinary, is xeno-aligned or just presents xeninely could identify as xenbinary. Xenbinary is different from xenogender, as xenic folks are aligned with xenine things. It's up for personal interpretations. Xenbinary could also represent ambinary individuals.
History
The term was coined by tumblr user imoga pride. The flag was made by tumblr user xenoleaf.