<prompt> The time interval time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease isGeneration timeIncubation periodLatent periodLag Phase  <response>: The incubation period is the time interval between invasion by an infectious agent and appearance of the first sign or symptom of the disease in question.Median incubation period: time required for 50 of the cases to occur following exposure.Latent period: The period from disease initiation to disease detection. Used in non-infectious diseases.Serial interval: The gap in time between the onset of the primary case and the secondary case is called the serial intervalGeneration time: The interval of time between receipt of infection by a host and maximal infectivity of that host.Secondary attack rate: Number of exposed persons developing the disease within the range of the incubation period. 