In the field of epidemiology, a sievert (Sv) is a unit of measurement used to quantify the health effect of ionizing radiation on the human body. It is a derived unit in the International System of Units (SI) and is named after the Swedish physicist Rolf Sievert. The sievert is used to measure the risk of radiation exposure, taking into account not just the amount of radiation absorbed, but also the biological impact of that radiation on human tissue.