Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. If it is lower than normal then it is called as low blood pressure or hypotension.
In physiology and medicine, hypotension is abnormally low blood pressure. This is best understood as a physiologic state, rather than a disease. It is often associated with shock, though not necessarily indicative of it. Hypotension is the opposite of hypertension, which is high blood pressure.