It's possible that "aa2.hair.v1" is a proprietary term, a code name, or an internal designation used within a specific organization or research group. Alternatively, it could be a relatively new term that has not yet been widely documented or publicized.
aa2g/AA2Unlimited: Modding framework for Artificial Academy 2 21 Jul 2023 — aa2.hair.v1
Custom shader setup enhances strand-like specular response, mimicking real hair. It's possible that "aa2