Apogender is a subset of agender in which one feels not only genderless but entirely removed from the concept of gender. It can be described as less than a lack of gender and more as having no connection, association, or relation towards the concept of gender as a whole.
Apogender can be considered an abinary, neutral, or unaligned gender as it doesn't fall under male, female, masculinity, femininity, or anything in between or derived from these things because it is entirely removed from the concept of gender.
It can be similar to cassgender where is it indifferent towards the idea of gender identity, but different, as cassgender individuals may experience gender identity (although it is unimportant to them).
Some would argue that apogender is not a subset of agender, that agender still refers to the concept of having a gender while being genderless or that being genderless is itself a gender. However, apogender is still related to the concept of agender as lacking a gender or being without gender and could be considered an agingender or agiaspec gender.
Apogender was coined on July 11, 2014 by queerspike, a since-deactivated Tumblr blog.
The flag was created by Tumblr user pastelmemer (now pastelroswell) on July 10, 2016. The meaning is unknown but it is possible that the green comes from the agender flag, and the black represents genderlessness.
Apo is a Greek word that means away from, separate, or at the farthest point.