Dispargender is when someone feels like they do have a gender, but it is missing. It is different from agender because they do not feel like they don't have a gender, just that the gender they did have is gone.
A similar term, exclusive to neurodivergent people, is caedogender.
History
The term was coined by Fandom user Lunarblema on January 14, 2021. The flag was created by the same user on the same day. The term was picked up by ChimpsModeNow after Lunarblema left.
Etymology
The prefix 'Dispar-' is based on the Romanian word dispărut, which means missing.