1. The process of maintaining the fertilized eggs of birds and of some reptiles and egg-laying mammals at the optimum temperature for the successful development of the embryos. A period of incubation follows the laying of the eggs and precedes their hatching.

2. The process of maintaining a culture of bacteria or other microorganisms at the optimum temperature for growth of the culture or of maintaining a reaction mixture at an appropriate or specified temperature.

3. The phase in the development of an infectious disease between initial infection and the appearance of the first symptoms.