clouds-mogai:

This is a fluid gender described as being empty/vacant, but having the capacity to be gendered.  

There are ways it can be “occupied,” including but not limited to being perceived as a certain gender (similar to custodiogender), thinking about a gender (similar to thoughtgender), or purposefully gendering it (similar to cinngender). The “occupied” feeling may or may not be temporary. One may or may not continue to identify as vacansgender if their gender is “occupied.”

It may be able to be any gender, but it might also be only available to specific genders, in which case you can replace the -gender with the appropriate label, e.g. vacansfin, vacansboy, vacansabinary, vacansfloren. 

The name comes from Latin for vacant, showing that at times/right now it is unoccupied, but it is available to be filled.