Blood Pressure is a measure of the blood flow through the veins.

it is represented as a ratio of 2 numbers:

Systolic Blood Pressure­ and Diastolic Blood Pressure

Systolic Blood Pressure is the TOP number

Systolic blood pressure measures is the pressure in the arteries when the heart beats

Diastolic Blood Pressure is the BOTTOM number

Diastolic blood pressure measures the pressure in the arteries when the heart is at rest

Blood Pressure is usually shown as a fraction of the Systolic over the Diastolic blood pressure

120/80 mm Hg

Source: American Heart Association