'瘦肥' (shòu féi) is a fixed noun phrase meaning 'thin and fat' — not as separate adjectives, but as a paired concept representing contrasting body conditions. The two characters are antonyms: 瘦 means 'thin' or 'lean', while 肥 means 'fat' or 'plump'. Together, they form a binomial expression often used in contexts where both extremes are observed simultaneously or comparatively — especially when describing physical variation within a group of animals, livestock, or sometimes people in informal or observational speech.

This term appears frequently in agricultural, veterinary, or rural settings — for example, when farmers assess herd health, or when describing uneven feeding outcomes. It carries no strong positive or negative connotation by itself, but functions descriptively rather than judgmentally. Unlike standalone adjectives, '瘦肥' is rarely modified by degree words (e.g., *very* or *quite*) and almost never used predicatively ('The cow is 瘦肥') — it only works as a noun phrase referring to the condition pair or the observable contrast.