What is the difference between a single crusted pie and a double crusted pie?

A Single Crust Pie is a dessert that does not have a top crust. It only has the bottom crust that lines the pie plate and holds the filling. The bottom crust is placed in the pie plate and the edges are trimmed. The edges are then crimped to provide the crust with a finished look. Many times a Single Crust is baked or partially baked before the filling is added. This prevents the crust from becoming too soggy when certain fillings are used. Even though a Single Pie Crust does not have a top crust, it will often have some type of topping added either as part of the pie or as it is served. Some of the common toppings used are meringue and whipped cream.

Double-crust pie: A pie made with both a bottom and a top crust. The first crust used for the Double Crust Pie is the bottom crust which is rolled out and placed in the pie plate. A filling is prepared and placed in the pie plate over the surface of the bottom crust. The top crust is then rolled out and placed over the top of the filling. The edges of the top and bottom pie crusts are trimmed and crimped to seal the crusts together. The top crust has several slits made into the crust or a few small holes punctured into the crust with a fork to allow steam to escape as the pie is baked.

http://www.recipetips.com/glossary-term/t--a/a.asp

Since the earliest colonial days, apple pies have been enjoyed in America for breakfast, for an entrée, and for dinner. Colonists wrote home about them and foreign visitors noted apple pie as one of our first culinary specialties. We cannot claim to have invented the apple pie, just to have perfected it.

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star_gazer -- Now THAT is priceless!!! Good one!!!

To me, it's a tart if it hasn't got a pastry top. Exceptions are shepherd's pie and the marine equivalent, which have potato toppings. Some meat-based pies may dispense with the base, but they have the top. Anything else is a tart, or a quiche - which is merely a savoury custard tart. Tart is so associated with sweet now that you couldn't sell steak and kidney tarts (should you really want to!).

Okay...here's the deal...as someone who is quite adept at NOT cooking OR baking...I offer the following: A top crust is usually applied when the pies have a sweet filling that requires heightened cooking.

Pecan pies and pumpkin pies do not use a second crust.

Apple, cherry, strawberry, rhubarb, etc. will use the second crust to enhance the cooking process.

https://en.wikipedia.org/wiki/Pies