The force that blood exerts against the wall of a vessel is called blood pressure.
This pressure is much greater in arteries than in veins. The pressure of blood inside the artery during ventricular systole (contraction) is called systolic pressure and pressure in the artery during ventricular diastole (relaxation) is called diastolic pressure.
The normal systolic pressure is about 120 mm of Hg and diastolic pressure is 80 mm of Hg.
Blood pressure is measured with an instrument called a sphygmomanometer.
High blood pressure is also called hypertension and is caused by the constriction of arterioles, which results in increased resistance to blood flow. It can lead to the rupture of an artery and internal bleeding.