肌理 literally combines 肌 (jī), meaning 'muscle' or 'flesh', and 理 (lǐ), meaning 'texture', 'grain', or 'principle'. Together, it refers to the natural, fine surface structure of skin or muscle — such as visible pores, lines, or subtle ridges — often observed in medical, artistic, or cosmetic contexts. It emphasizes organic, microscopic detail rather than broad appearance.

Beyond biology, 肌理 is frequently used metaphorically in art criticism and literature to describe the delicate, intrinsic texture of materials like wood grain, stone surfaces, ink wash painting strokes, or even the 'textural quality' of language or music. It conveys a sense of subtle, layered complexity that invites close observation. While rooted in physiology, its usage extends into aesthetics and sensory description, always implying an inherent, fine-grained structure.