What is the medical term for low blood pressure? 

Low blood pressure is generally considered a blood pressure reading lower than 90 millimeters of mercury (mm Hg) for the top number (systolic) or 60 mm Hg for the bottom number (diastolic).

Hypotension is low blood pressure. Hypotension is a condition in which the blood pressure is lower than normal, which can result in symptoms such as dizziness, fainting, and fatigue. While low blood pressure can be a sign of good cardiovascular health, it can also indicate an underlying health problem, such as dehydration, heart problems, or endocrine disorders. In some cases, it may be treated with medications, lifestyle changes, or other treatments, depending on the cause.

Ideal blood pressure is considered to be between 90/60mmHg and 120/80mmHg. High blood pressure is considered to be 140/90mmHg or higher and low blood pressure is considered to be below 90/60mmHg.