A cohort study in scientific research is an observational study design where a group of individuals, known as a cohort, is followed over time to assess specific health outcomes or effects of exposures. Researchers may track individuals who share similar characteristics, such as age, experiences, or exposures, to evaluate how these factors influence health. These studies can provide valuable data on risk factors, disease progression, or the effectiveness of interventions, and they are commonly used in epidemiology and public health research.