Atriboy, atrinboy, or atrinaboy, refers to an atrinary boy.
As the definition of atrinary states, it is referring to any genders that are completely unrelated to maleness, masculinity, femaleness, femininity, neutrois-ness, or neutrality, and is nowhere in between those things, while not necessarily feeling genderless.
The gendered part of themselves is being a boy. Someone who is a atriboy may feel as if they're a boy while not being related to maleness, masculinity, femaleness, femininity, neutrois-ness, or neutrality, and feels as if they're nowhere in between any of them.
This could be due to feeling a connection to boyhood rather than maleness, inherently. A atriboy may feel as if they're a boy while also not being a part of the gender trinary.
The -girl counterpart to this gender is atrigirl.
History
This gender was coined by Reddit user u/hiitsyaz in August, 2021, with no exact date.
Atriboy was coined due to wanting to show how differently one can experience their gender(s), due to how (stereotypically) masculinity is associated with being a boy. This isn't the case though, as you can present however you want too, regardless of your gender(s).
Etymology
The multitude of names of this gender are a combination of atrinary and girl, which were also coined by the same Reddit user.