Final answer:
Systolic pressure is the pressure in the arteries when the heart ventricles contract, typically measuring around 120 mm Hg in healthy adults.
Step-by-step explanation:
The characteristic of systolic pressure is that it is the pressure during heart contraction. Specifically, when the ventricles of the heart contract during the phase known as systole, blood is ejected into the arteries resulting in the highest pressure within the cardiovascular system. This pressure, typically around 120 mm Hg in a healthy adult, is crucial for maintaining blood circulation throughout the body. Conversely, diastolic pressure is the pressure during heart relaxation, or diastole, when the ventricles are filled with blood. The systolic value is always the higher value and usually precedes the diastolic value when blood pressure is written down, for instance, as '120/80 mm Hg'.