Recently we came across such an expression lèvres en retrait. I have explored all Internet resources, but unfortunately I could not find the answer. Could anyone explain the meaning of this phrase?
"lèvres" means "lips" or "labium", it should be obvious with more context which one this is about. "en retrait" is synonym with "reculé", "enfoncé", "qui se tient à l'écart".
so "lèvres en retrait" could be part of the physical description of someone's face. It is difficult to say more without a more precise context.