“酸” (suān) is the Chinese word for "sour." It describes a taste that is often associated with foods like lemons and vinegar. This flavor is one of the five basic tastes, alongside sweet, bitter, salty, and umami. Sourness is typically caused by the presence of acids, such as citric acid in citrus fruits or acetic acid in vinegar. In addition to its culinary significance, “酸” can also refer to the chemical property of acidity. Acids are substances that can donate protons (H⁺ ions) in a solution. Common examples include 盐酸 (hydrochloric acid) and 硫酸 (sulfuric acid), which are used in various industrial applications and laboratory settings.