Final answer:
Incidence is the number of new disease cases that occur within a period of time, while prevalence includes both new and existing cases of a disease in a population over time.
Step-by-step explanation:
In the context of disease, incidence is the number of new cases of a disease that occur within a defined time period, usually a year. It measures the risk of developing the disease. Prevalence refers to the total number of both new and existing cases of a disease in a population over time. It provides an indication of the overall health of the population during that time period.