Systolic: The blood pressure when the heart is contracting. It is specifically the maximum arterial pressure during contraction of the left ventricle of the heart. The time at which ventricular contraction occurs is called systole.
In a blood pressure reading, the systolic pressure is typically the first number recorded. For example, with a blood pressure of 120/80 ("120 over 80"), the systolic pressure is 120. By "120" is meant 120 mm Hg (millimeters of mercury).
"Systolic" comes from the Greek systole meaning "a drawing together or a contraction." The term has been in use since the 16th century to denote the contraction of the heart muscle.