Audi and VW's first generation of direct-injected engines, under the Fuel Stratified Injection (FSI) moniker, have a high-pressure fuel pump in the engine bay. The pump lives high on the engine, and a piston in the pump is driven by an extra lobe on the end of the intake camshaft. 

This part, what VW calls the "cam follower", sits between the fuel pump and the camshaft, and it keeps the piston from directly wearing down the cam lobe. Because it presses against the rotating camshaft, this follower will itself eventually wear out; if the fuel pump piston runs directly on the camshaft, it'll damage both.

This particular cam follower is made by the Original Equipment Manufacturer to VW for this part, INA. We recommend checking this follower with every other oil change (about every 10000 to 15000 miles) and replacing it when it's worn. We suggest replacing the three fuel pump bolts at this time as well.