The word circulation refers to the movement of blood through your body's blood vessels and heart. It can also mean free movement in a more general sense, as in the circulation of news, money, or even library books.
Circulation of blood is what happens in your body's circulatory system. There are other kinds of circulation too, like sap moving through a plant, air moving freely within a building, or even party guests strolling around your living room. The key thing they all have in common is orderly movement. The Latin root, circulare, means "to form a circle."