Errgender is a xenogender in which the person feels that their gender is somewhat "stray" and that they are unable to get a hold of it or fully understand it.
History
Errgender was coined on July 13, 2014 by tumblr user eaglestrike (gayquicksilver as of 2019).
Flag
The flag was created on January 19 2018 by Pride-Flags on Deviantart.
Etymology
The word Errgender comes from the Latin prefix err-, which means for something to be stray, or deviated.