皮 is a pictograph showing a hand (又, the right side of the character) holding a knife and stripping away an animal's hide. The oracle bone form clearly depicts the action of skinning. From this concrete butchery scene grew the abstract meaning: the result of stripping = the hide / skin / outer covering. By further extension, 皮 came to mean any surface, peel, rind, or outer layer — not just animal hide. As a radical, 皮 itself appears in characters like 皺 (zhòu, wrinkle), 疲 (pí, tired — exhausted "to the skin").

Korean reading "pi." 皮膚 (pibu, skin — medical / formal), 脫皮 (talpi, molting / shedding skin — used metaphorically for personal transformation), 毛皮 (mopi, fur), 樹皮 (supi, tree bark), 表皮 (pyopi, outer skin / epidermis — both anatomical and metaphorical for "surface appearance"), 皮革 (pihyeok, leather goods).

Mandarin pí, 2nd tone. 皮 (pí, skin / leather / surface), 皮肤 (pífū, skin), 脱皮 (tuōpí, to peel / molt), 肚皮 (dùpí, "belly skin" = the stomach exterior), 苹果皮 (píngguǒpí, apple peel). And the wonderfully colloquial 调皮 (tiáopí, "to play with skin / to dye-treat hide" → "mischievous / cheeky") — a top-frequency adjective for describing children's playful naughtiness in Chinese: 这个孩子很调皮 ("this kid is so cheeky").

Japanese on-reading ヒ (hi) — 皮膚 (hifu, skin — medical), 表皮 (hyōhi, epidermis), 脱皮 (dappi, molting). Kun-reading かわ (kawa) — 皮 (kawa, skin / peel / hide). Important homophone caution in Japanese: かわ also means "river" (written 川) — same kana sound, different kanji. Context distinguishes 皮 (kawa, peel) from 川 (kawa, river). Compounds: 毛皮 (kegawa, fur — note this mixes kun-reading 毛 ke + kun-reading 皮 kawa with rendaku to gawa).

Memory aid: a hand stripping away an animal's hide. From the action of skinning came the result (skin) and by extension all outer surfaces, peels, and rinds.