A pie crust shield is an aluminum or silicone ring used when baking an open-faced pie; it covers the pie crust but not the pie filling. It is used when the pie crust is done cooking and is at risk of burning, but the pie filling still needs more time.

This appears to be a modern invention, as historically the pie crust was not seen as something that needed to be eaten, with the crimped edges of the pie crust existing for primarily functional or decorative purposes.

Most people, if they use anything, will just use aluminum foil.