A spore is a reproductive cell produced by plants (fungi, moss, ferns) and some protozoa and bacteria. The spore develops into an adult, often after a state of dormancy or hibernation.

Certain bacteria produce spores as a defensive mechanism. Bacterial spores have thick walls, and are able to withstand varying temperatures, humidity, and other unfavorable conditions.

Chemical disinfection kills bacteria, but does not destroy their spores. Sterilization destroys spores as well as bacteria, and requires high temperatures and high pressures. In health-care settings, sterilization is usually accomplished using a device called an autoclave.