Docking
Docking is pricking pastry all over with a fork or a spiked roller so steam can escape during baking and the pastry stays flat.
Without docking, pockets of steam lift the pastry into bubbles that set unevenly. It matters most on blind-baked bases and any flat sheet of pastry baked on its own.
Do not dock a pie lid. A lid needs only a vent or two; docking it all over lets the filling's moisture escape too fast and dries the pie.