A cohort study is a type of research design that follows a specific group of individuals over a period of time to observe various outcomes or changes in health status. Cohort studies can be either prospective, where researchers follow a group of people forward in time, or retrospective, where researchers examine data from past records. This type of study allows researchers to analyze the relationship between exposures or risk factors and the development of certain diseases or outcomes. Cohort studies are often used to investigate the cause and effect relationships in epidemiology and can provide valuable evidence for guiding public health interventions and policies.