What is the difference between incidence vs. prevalence?

According to the New York State Department of Health, incidence is used to measure a patient's likelihood of being diagnosed with a disease during a period of time, while prevalence is used to measure a patient's likelihood of already having a disease. Incidence and prevalence are statistical terms.

"Incidence rate" is the number of newly diagnosed patients divided by the number of "at-risk" persons, whereas "prevalence rate" refers to the total number of patients within a population divided by the total population. In addition to incidence and prevalence, morbidity and mortality are also statistical terms used to describe how a disease has affected a given population.