胰皂 (yí zào) literally means 'pancreas soap' — a historical term referring to glycerin soap, originally made by saponifying animal fats (including pancreatic tissue) with alkali. Though modern glycerin soaps rarely contain actual pancreas, the name persists as a traditional label for mild, moisturizing soaps rich in glycerin, often used for sensitive or dry skin.

This word is primarily found in older product names, traditional pharmacy contexts, or nostalgic branding; it's not commonly used in everyday speech today. It carries a connotation of naturalness and gentleness, contrasting with harsher synthetic detergents. Learners should recognize it mainly in written contexts — on vintage packaging, herbal medicine labels, or historical texts — rather than expect to hear it in conversation.