Systolic pressure is the pressure in the arteries (blood vessels carrying oxygenated blood) when the heart contracts (systole
). Systolic pressue will be higher.
The pressure in the arteries fall when the contraction is over and the heart is relaxing (diastole) as no blood is being pumped into them during diastole. The pressue then is called diastolic pressure and will be lower.
The difference between the two values is known as pulse pressure.