Atrigirl, atringirl, or atrinagirl, refers to an atrinary girl, this is also atribinary.
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 girl. Someone who is a atrigirl may feel as if they're a girl 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 girlhood rather than femaleness, inherently. A atrigirl may feel as if they're a girl while also not being a part of the gender trinary.
History
This gender was coined by Reddit user u/hiitsyaz in August, 2021, with no exact date.
Atrigirl was coined due to wanting to show how differently one can experience their gender(s), due to how (stereotypically) femininity is associated with being a girl. This isn't the case though, as you can present however you want too, regardless of your gender.
Etymology
The multitude of names of this gender are a combination of atrinary and girl, which were also coined by the same person.