What is the definition or description of: low blood pressure?

Caution: Low BP may have a good connotation or it may carry risk. It's important to check BP sitting and standing; it reflects ones state of hydration. Normally-hydrated people have little change in BP with standing; with standing, BP falls if dehydrated; it rises if salt/fluid overload. BP is low (but still healthy) if the systolic is 90-105. However, it is too low if one feels dizzy at that BP.