疾病潜伏期是接触病原体（可以是微生物或者是化学制剂、辐射等）后，症状和体征有明显的表现前所经过的时间。疾病潜伏期可能短至只有几分钟，或者长达几十年（克雅氏病大概为30年）。潜伏期内的传染病同样具有传染性。

Incubation period is the time elapsed between exposure to a pathogenic organism, a chemical or radiation, and when symptoms and signs are first apparent. In a typical infectious disease, incubation period signifies the period taken by the multiplying organism to reach a threshold necessary to produce symptoms in the host.