Blood pressure is defined as the force of blood on vein walls and is measured in milligrams of mercury. It is represented by two numbers - systolic, which is the pressure during heartbeats, and diastolic, which is the pressure between heartbeats. Blood pressure categories in adults include normal, prehypertension, and hypertension based on systolic and diastolic levels. Hypertension often has no symptoms so it important to get tested using a sphygmomanometer and stethoscope. Prevention tips include eating a healthy diet high in fruits and vegetables and low in fat, maintaining a healthy weight, and exercising regularly.