v: to pass from one point throughout a system and back to the starting point. For example, drilling fluid is circulated out of the suction pit, down the drill pipe and drill collars, out the bit, up the annulus, and back to the pits while drilling proceeds.

To permit the drilling fluid to go down through the drill string and well bore while drilling operations are temporarily suspended. This is done to condition the hole and the well bore before drilling continues, in order to prevent friction between the metal walls of the hole and the casing (that is, prevent metal rubbing against metal.)

To pump drilling fluid into the borehole through the drillpipe and back up the annulus.

To pass from place to place, from person to person, or from hand to hand; to be diffused; as, money circulates; a story circulates.

To cause to pass from place to place, or from person to person; to spread; as, to circulate a report; to circulate bills of credit.

become widely known and passed on; "the rumor spread"; "the story went around in the office"

Materials that can be removed from the premises, or checked-out, may circulate. Reference books, or items in special collections, do not circulate.

This is what it's called when a book is checked out. Most of the library material which is checked out can be taken from the building, but some such as reserve material must be used in the library. Other items may not circulate at all. Items which often do not circulate are reference books, periodicals, and expensive or rare items.

Materials which can be charged are said to circulate.

To move in a circle or circuitously; to move round and return to the same point; as, the blood circulates in the body.

move through a space, circuit or system, returning to the starting point; "Blood circulates in my veins"; "The air here does not circulate"

move in circles

To distribute in accordance with a plan. See DISSEMINATE.

cause to be distributed; "This letter is circulating among the faculty"