A xenogender is any gender which isn't male or female, and doesn't fit along the male-female axis of gender. So, for non-xenogender identities you have: man, woman, demiboy, demigirl, agender, bigender (male and female), genderfluid (male and female), genderfae (female and agender), genderfaun (male and agender), androgynous, and, you know, everything in that whole space.

Xenogenders are genders which don't exist in relation to binary gender or the absence of gender. Unfortunately, they're harder to name, because you don't get to pick a name that relates to existing terms for binary gender. The most common path is to name a gender through analogy. For example: suppose you were trying to explain male gender to an alien creature who's never heard of maleness or masculinity. So you say "Men are meant to be strong, and to have camaraderie, and to be protectors, and to have interest in athleticism". So you try to come up with a single word to relate all this quickly, and maybe you settle on the term "shieldgender". So in the absence of the word "man", you have that. Now imagine trying to explain a xenogender to a binary person. There's cloudgender, and seagender, and robotgender, and pretty much any set of interrelated concepts you can imagine.

For my xenogender, it's more literal and less analogous. People of my gender relate to one another through a swarm dynamic instead of a nuclear family, so we're swarmgender. It's just a description of how we work.