TT #68 · Parshas Tazria · Aliyah 1 · Passuk 2
English: When a person has on the skin of the body a swelling, a rash, or a discoloration, and it develops into a scaly affection on the skin of the body, it shall be reported to Aaron the priest or to one of his sons, the priests.
Chabad.org — Chumash, English translation + Rashi for Vayikra 13:2
Torah Temimah cites Shevuos 6b for the description of baheres as a deep-appearing white affliction.
E-Daf — Shevuos 6b · Shas.org · Sefaria — source text and translation
English: The Sages taught: baheres is described as deep, as Scripture says, “its appearance is deeper than the skin,” like the sun, which appears deeper than the shade.
Definition by analogy
The Gemara interprets the biblical description of the appearance as deep by analogy to the sun's appearance relative to shade.