Invisigender is a gender that feels, for whatever reason, partially or fully invisible. It can be used as a prefix for other genders, such as invisigirl, invisiboy, invisinonbinary, etc.
It may mean that ones gender identity is complex and cannot be understood by other people.
History
Invisigender was coined by Tumblr user Gendermark (now deactivated) on or before July 14 2014[1].