TT #227 · Parshas Tazria · Aliyah 7 · Passuk 42
English: But if a white-reddish lesion appears on the bald area or the front bald area, it is an eruptive tzaraas on his bald area or front bald area.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:42
Torah Temimah cites Sifra (Toras Kohanim) for the definition of gabachas as the bald area sloping forward from the crown.
Sifra — Vayikra 13, Midrash Sefer
English: The Sifra defines gabachas as the bald area that slopes forward from the crown.
The Sifra defines the anatomical area called gabachas.
Gabachas is the frontal bald area, where the head slopes forward from the crown.