Baking blind (sometimes called pre-baking) is the process of baking pastry without the filling. Blind baking a pie crust is necessary when it will be filled with an unbaked filling (such as with pudding or cream pies) or when the filling has a shorter bake time than the crust. Blind baking a pie crust also helps prevent the pie crust from becoming soggy from its filling.
Generally, the pie crust is lined with tin foil or baking paper, then filled with pie-weights to keep the crust's shape while baking . These weights are usually ceramic or metal , but dried pulses can be used as as well as rice. The crust is docked with the tines of a fork to produce small holes—this helps steam escape and prevents the crust from bubbling up.
Blind-baking also helps to form a nice pastry case for the filling as it has already been partially formed from blind-baking. (thanks Wikipedia!)