Incidence is a term used in epidemiology to refer to the frequency of occurrence of a particular event or condition within a specific population over a specified period of time. It is typically expressed as the number of new cases of a disease or health outcome that develop within a population at risk during a certain time period. Incidence is an important measure in public health research as it helps to understand the rate at which diseases or health conditions are developing in a population, which can inform preventive measures and healthcare interventions.