The process of maintaining constant temperature, humidity, and other environmental factors for the purpose of allowing an embryo to develop properly within an egg, a prematurely-born infant to continue its development outside of its mother's womb, or microbe or tissue cultures to grow until they are a scientifically or medically useful size. When done artificially, incubation is done within an "incubator." The period between the initial infection of a host by a microbe and the time that symptoms begin.