Alimull, or alimüll, is a term to describe any transgender or cisn't person who is AFAB. It was created to encourage using alternative language to how many people use AFAB, especially in the context of non-binary people, that reduces them to their assigned gender. Though there had been words to describe a variety of AFAB transgender experiences, such as transmasculine or trans men, there had not yet been a term to describe the shared experience of the intersection of being both transgender and AFAB for all people who have both of those labels. This includes, but is not limited to, AFAB non-binary people, AFAB binaryn't people, AFAB xenogender people, AFAB multigender and genderfluid people, transmasculine people, and trans men.
Transmasculine, though similar to alimull, does not encompass the experiences of all AFAB transgender people, such as AFAB non-binary people who do not use alignment labels, feminine-aligned AFAB binaryn't people (such as demigirls), and AFAB transgender people who are xenogender or use other alignment labels that transcend feminine- or masculine-aligned. It is thus not accurate enough to generalize or simplify the AFAB trans experience into the label of transmasculine, though many alimull people are transmasculine as well.
It is important to clarify the different experiences of AFAB and AMAB transgender people in some situations, such as discussion of transphobia and how it can differently manifest towards AFAB vs. AMAB transgender people. For example, alimulls may experience transphobia in the sense of infantilization and one not knowing their "real" identity due to them being AFAB (and the experience similar to misogyny for all AFAB people). In common TERF rhetoric, such as J.K. Rowling's now infamous transphobic essay, there is the idea of being "concerned" for the "misguided girls", and the idea that being transgender is a way to escape patriarchal oppression. However, those specific transphobic ideas are not ones directed at aliwolffs (AMAB transgender people).