Ningender (shortened to NIN) is an umbrella term for all genders which are neutral/non-binary in nature (NIN). It can be used as an umbrella term for any genders that are primarily related to a gender that is not masculine nor feminine. This includes genders such as neutrois, stellarian, maverique, and other unaligned non-binary genders among others.
NIN is not synonymous with non-binary, because some non-binary genders can be feminine or masculine aligned. For example, juxera is a non-binary gender but it is feminine in nature, not neutral.
Ningender can also be used as a gender on its own, referring to any gender that isn't fully defined by being neutral but is still related to neutralness, or a gender in which neutralness is its defining feature. It's often used by people who cannot narrow down their gender any more than being neutral or non-binary.
The masculine equivalent is mingender. The feminine equivalent is fingender.