Maingender is an umbrella term for all genders which are male in nature (MAIN). It can be used as an umbrella term for any genders that are partially or fully related to manhood or maleness. Maingenders may or may not also be related to masculinity (mingenders). The term is similar to miaspec and wergender.
Maingender can also be used as a gender on its own, referring to a gender in which maleness is a defining feature or the primary feature, but is not binary male. It's may be used by people who cannot narrow down their gender any more than being related to male, but not a binary man.
The female equivalent is feingender.