The amount of blood circulating throughout the body, typically about 5 liters for an adult.
The total amount of blood in the circulation.
This is the amount of blood circulating throughout the body.
Blood volume is the volume of blood (both red blood cells and plasma) in a person's circulatory system. A typical adult male human has a blood volume of some five liters http://hypertextbook.com/facts/1998/LanNaLee.shtml. Blood volume is regulated by the kidneys.