胃酸 (wèi suān) literally combines 胃 (wèi), meaning 'stomach', and 酸 (suān), meaning 'acid' or 'sour'. Together, they refer to the hydrochloric acid secreted by gastric glands in the stomach lining, essential for digesting food and killing harmful bacteria. It is a core term in medical and health-related discussions in Chinese.

In everyday usage, 胃酸 often appears in contexts related to digestive discomfort — such as excess stomach acid causing heartburn, acid reflux, or gastritis. People may say 胃酸过多 (wèi suān guò duō, 'excess gastric acid') or take medicine to 'reduce gastric acid'. While technically a biological substance, it’s rarely used in abstract or metaphorical ways — always grounded in physiology or clinical experience.