免疫 (miǎn yì) literally means 'to avoid disease' — 免 (miǎn) means 'to avoid, exempt, or spare', and 疫 (yì) refers to 'epidemic, plague, or infectious disease'. Together, they form the scientific term for 'immunity': the body's ability to resist or eliminate pathogens like viruses and bacteria. This word is used broadly in medical, biological, and public health contexts, such as discussing vaccines, immune systems, or autoimmune disorders.

The term appears frequently in news reports about pandemics, health education, and clinical discussions. It can function as a standalone noun ('have strong immunity') or combine with modifiers (e.g., 免疫系统 'immune system', 免疫力 'immune capacity', 获得性免疫 'acquired immunity'). Unlike colloquial terms like 抵抗力 (dǐ kàng lì, 'resistance'), 免疫 carries formal, technical weight and is rarely used in casual daily speech without supporting context.