Mentocervical Angle
the chin-to-neck line that decides whether your profile reads sharp or soft
Grounded in the research on Wikipedia: Cervicomental angle; clinical facial-aesthetic anthropometry (Powell & Humphreys, 1984)
step 1 - name it
Mentocervical angle is the line your profile makes from chin (mentum) down to the front of your neck (cervix). Surgeons measure the closely-related cervicomental angle and like it around 90-120 degrees. Tighter and more defined reads as a sharp jaw; open and soft reads as a weak chin or 'double chin' even when you're lean. It's a side-profile thing, not a front-facing one.
step 2 - trace the science
This is real clinical anthropometry, not a forum invention. Plastic surgeons like Powell and Humphreys (1984) mapped 'ideal' profile angles to plan chin and neck work, and the cervicomental angle is a standard pre-op measurement for chin implants, neck lifts and submental liposuction. So the term is legit medicine. What's NOT legit is the looksmaxxing claim that you can will this angle tighter at home.