I have the need to describe, in a technical document, the particular portion of a star here highlighted red (or any of the other like areas):
The width of each
…?shall be eight units at the point where they meet.
While in the title of this question I describe it as an arm, given the formal context of my intended usage, I'm loath to use such, as it seems an informal or slang term. Likewise, as I will be describing the dimensions of this section, using a term such as point seems inappropriate, as I would typically view that as referring to the vertex itself, not the area between the convex and concave vertices.
I've done some searches for arm and lobe, but can't seem to find any examples of their usage in this context. Is there a formal, proper, or technical term for this particular area of a star?