prevalence
n. the total number or percentage of cases (e.g., of a disease or disorder) existing in a population, either at a given point in time (point prevalence) or during a specified period (period prevalence). For example, health researchers may want to investigate the prevalence of a new disease in an area, whereas education researchers may be interested in the prevalence of bullying or cheating among students of a certain age group. See also incidence.