Flow control refers to the control of oil flow into or out of a circuit. Flow control valves are often used to regulate the speed of an actuator or to divide flow between two or more circuits. There are many types of flow control valves, including a fixed orifice, a variable orifice (such as a needle valve), or pressure compensated valve arrangements.
The example shown is a pressure compensated flow control valve. Note that the flow control valve above the orifice is slightly open, directing a small portion of flow to tank. This action is a result of the pressure difference across the orifice. The cylinder speed will be reduced due to the reduction of flow through the flow control valve