What is blood pressure and what does hypertension mean

Blood pressure (BP) is the pressure exerted by circulating blood upon the walls of blood vessels. It is usually measured at a person's upper arm by an instrument called sphygmomanometer.  Blood pressure is usually expressed in terms of the systolic (maximum) pressure over diastolic (minimum) pressure and is measured in millimetres of mercury (mm Hg). It is one of the vital signs along with respiratory rate, heart rate, oxygen saturation, and body temperature. Normal resting blood pressure in an adult is approximately 120/80 mm Hg. 

Systolic pressure is the pressure or force the heart places on the walls of your blood vessels as it is working/pumping with each heartbeat. Diastolic pressure (the second and lowest number) is the lowest pressure the blood places on the walls of your blood vessels when the heart is relaxed between beats.

Both of these measurements are important. A high systolic pressure indicates strain on the blood vessels when the heart is attempting to pump blood into bloodstream. If your diastolic pressure is high, it means that your blood vessels have little chance to relax between heartbeats. The pulse pressure is the difference between the measured systolic and diastolic pressures
 
Blood pressure varies depending on situation, activity, and disease states. It is regulated by the nervous and endocrine systems. Blood pressure that is low due to a disease state is called hypotension, and pressure that is consistently high is hypertension. Hypertension (HTN or HT), also known as high blood pressure or arterial hypertension, is a chronic medical condition in which the blood pressure in the arteries is persistently elevated. Hypertension usually does not cause symptoms initially, but sustained hypertension over time is a major risk factor for hypertensive heart disease, coronary artery disease, stroke, aortic aneurysm, peripheral artery disease, and chronic kidney disease.

Hypertension is classified as either primary (essential) hypertension or secondary hypertension. About 90–95% of cases are categorized as primary hypertension, defined as high blood pressure with no obvious underlying cause. The remaining 5–10% of cases are categorized as secondary hypertension, defined as hypertension due to an identifiable cause, such as chronic kidney disease, narrowing of the aorta or kidney arteries, or an endocrine disorder such as excess aldosterone, cortisol, or catecholamines.