Immune means protected from something harmful, especially a disease. When you're immune to chickenpox, your body has learned to fight off that virus so you probably won't get sick from it, even if you're exposed to someone who has it.

Your body becomes immune through experience or vaccination. After you recover from chickenpox, your immune system remembers how to defeat that virus, often making you immune for life. Vaccines work similarly: they teach your body to recognize and fight diseases without making you actually sick first.

The word also means being protected from other unwanted things. A witness in a trial might receive immunity from prosecution, meaning they can't be charged with a crime in exchange for their testimony. Teachers aren't immune to making mistakes, meaning they can mess up just like anyone else. When something is described as “not immune to,” it means it can still be affected.

Your immune system is the network of cells and organs in your body that fights off infections and diseases. Doctors who study diseases and the immune system are called immunologists. Anything that relates to the immune system is called immunological.