Torque Converter Clutch (TCC)
WARNING: This page is about a different car, the 2004 Pontiac Sunfire, 2004 Chevrolet Classic, and 2004 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
Apply fluid is routed to the torque converter at the same time that release fluid exhausts from the converter. Apply fluid pressure applies the TCC.