Blood pressure refers to the force exerted by blood against the walls of the arteries as it circulates through the body. It is measured in millimeters of mercury (mmHg) and is recorded as two numbers - the systolic pressure (the pressure when the heart beats) over diastolic pressure (the pressure when the heart rests between beats). Normal blood pressure is considered to be around 120/80 mmHg, with lower or higher readings indicating high or low blood pressure respectively. Blood pressure can fluctuate throughout the day and can be affected by various factors such as stress, exercise, diet, medications, and medical conditions. Regular monitoring of blood pressure is important for maintaining good health and preventing complications like heart disease, stroke, and kidney damage.