In medical language both the terms are described as follows.
high blood pressure or prehypertension
High blood pressure increases the risk of heart failure, heart attack, stroke, and kidney failure
Low blood pressure or hypotension,
low blood pressure can cause symptoms of dizziness and fainting or mean that they have serious heart, endocrine or neurological disorders. Severely low blood pressure can deprive the brain and other vital organs of oxygen and nutrients, leading to a life-threatening condition called shock.