Pie weights are small, heavy objects used to prevent pie crusts from puffing up or shrinking during baking. They help maintain the shape of the crust, ensuring even cooking and a perfect texture. Typically made of materials like ceramic, metal, or glass, pie weights are placed on top of parchment paper or aluminum foil inside the crust before baking. This technique, known as "blind baking," is essential for recipes that require a pre-baked crust, such as quiches or fruit pies.