Masculenby is a term for any sort of non-binary/man gender identity. It includes things such as demiboy, xoy, enboy, genderfaun, non-binary/boy bigender, and anything else.[1] It's an overarching term for anyone in those groups, especially if one swaps between them often, use multiple labels, or is unsure of the specifics of their identity but know they're some form of non-binary and girl.
Masculenby people may or may not have other genders that are not non-binary or man.
Feminine version of this is feminenby.
Resources
Original definition and flag by rouge-the-bat on Tumblr
Second flag made by IAmArtemisTheCat on LGBTA Wiki.