High blood pressure is a condition where the force of blood pushing against the walls of the arteries is higher than the normal range.  If your blood pressure rises and stays high over time, it can damage the body in many ways.  The National Heart Lung and Blood Institute states that 1 in 3 adults in the United States has high blood pressure.

While having high blood pressure does not immediately present an issue, over time, high blood pressure is known to damage the heart, your kidney, blood vessels, and other parts of you body.  This condition can lead to coronary heart disease, strokes, kidney failure, and other diseases.

Blood pressure is measured with two numbers:

    -Systolic blood pressure is the pressure when the heart beats while pumping blood, and
    -Diastolic blood pressure is the pressure when the heart is at rest between beats.

Normal systolic blood pressure is less than 120mmHg  and diastolic blood pressure is 80mmHg.

For more information:

http://www.nhlbi.nih.gov/health/dci/Diseases/Hbp/HBP_WhatIs.html