Facial Harmony
it's not one perfect feature, it's whether they agree with each other
Grounded in the research on Wikipedia: Facial symmetry / Physical attractiveness; looksmaxxing subculture
the setup
Facial harmony is the looksmaxxing word for proportion: how your features sit relative to each other, not how good any single one is. The claim is that a face reads as attractive when nose, eyes, jaw and midface are in balance, so a 'great jaw' on a recessed midface still looks off. Less about one trophy feature, more about whether the whole thing agrees with itself.
the real science
The grounded part is old: symmetry and averageness. Langlois & Roggman (1990) showed composited 'average' faces get rated more attractive, and meta-analyses since find symmetry has a real but small effect. 'Harmony' as a precise ranking system, though, is forum coinage, not a clinical measure. Surgeons use proportion guides, but the blackpill version that scores you to the decimal is way more confident than the evidence.