Blind baking refers to pre-baking a pie crust before adding the filling.  To blind bake, line the crust with parchment paper (or foil) and fill it with pie weights. This step helps to prevent the crust from shrinking during baking. Pie weights are ceramic or metal beads that are used to weigh down the unbaked crust.  They are widely available in most kitchen or home goods stores.  But it isn't necessary to go out and purchase pie weights.  Dried beans, rice, or uncooked popcorn kernels work just fine.  Although, if used, these items cannot be cooked and eaten afterward.  Instead, store them in a container and reuse them for blind baking.