Circulation

Circulation may be used in reference to:

Circulatory system, a biological organ system whose primary function is to move substances to and from cells
Circulation (fluid dynamics), the path integral of the fluid velocity around a closed curve
Exhaust gas recirculation, a nitrogen oxide reduction technique
Atmospheric circulation, the large-scale movement of air
Newspaper circulation, the average number of copies of a newspaper distributed on a day
Magazine circulation, the average number of copies of a periodical distributed per edition/ volume
Library circulation, the activities around the lending of library books and other material to users of a lending library
Circulation (currency), the transfer of currency through the hands of civilians