It is important to try and aim for your body's ideal blood pressure. Blood pressure, by definition, is how much force the blood exerts on the arteries' walls. This force is measured in mmHg (millimeters of mercury) or kPa (kilopascals).
Two values are usually given when you measure your blood pressure. The first is a systolic reading, given when the heart contracts, and a diastolic reading, given when the heart relaxes.
According to the Heart and Stroke Foundation, ideal blood pressure for a healthy adult is 120 mmHg / 16 kPa systolic, and 80 mmHg / 11 kPa diastolic (often written in as 120/80 in mmHg).
Slight variations of these readings are still healthy; blood pressure often increases or decreases due to a variety of factors like stress, diet, drugs and illness. It is when your blood pressure is drastically over or under those ideal blood pressure readings that there is cause for concern.
Blood pressure over 130/80 is over your ideal blood pressure and is concerned high. Such high blood pressure is called hypertension. Blood pressure lower than 90/50 is well under your ideal blood pressure and is called hypotension.
If your blood pressure reads 130/80, you have Prehypertension. 140/90 is Stage 1 Hypertension and 160/100 is Stage 2 Hypertension, a very serious condition. Try to keep your blood pressure within the ideal blood pressure range.