Tarts and pies are so similar that people often confuse one with the other. Both are baked in a pan and have a crust covering the bottom and sides. The crust is topped with all different kinds of fillings, from sweet ones such as fruit, cream, chocolate, and custard, to savory ones such as meat, cheese, and eggs. However, there are subtle differences between tarts and pies. First, tarts only have a bottom crust and never have an additional top crust that covers the filling like some pies. Because the filling is out in the open, chefs try to make it as attractive as possible, such as arranging fruit in overlapping circles. Second, tarts generally have straight sides and are shallower while pies have concave sides and are deeper. Third, a pie has more filling compared to the crust and the filling is often considered to be the most important part of the dessert. Tarts tend to have less filling and a slightly thicker crust, and the quality of the crust is considered just as important if not more important than the filling.
Tarts have been enjoyed at least as far back as medieval times. Many sweet and savory tart recipes can be found in medieval cookbooks. Below, Webster informs us that the word "tart" comes from the Old English word "tarte" (such as Tarte Tatin, an apple tart from France). The word "tarte" is itself derived from the Latin word "torta" for twisted. Therefore, tarts got their name because the dough for their crust was twisted or rolled before placing it in the pan.
Tarts are baked in metal pans similar to pie pans. The pans generally come in three sizes, a 9 1/2 to 10 inch diameter pan for creating a large tart to serve guests, a 3 to 4 inch diameter pan called a "tartlet" for individual dessert servings, and a 1 1/2 inch diameter small pan for appetizer portions. The largest tart pans normally have a removable bottom that makes it easy to remove the tart from the pan for a more attractive presentation. Additionally, the pans with the removable bottoms are somewhat easier to clean.
yclept also reminds me about "the ever popular rustic tart, made free form on a flat baking sheet! Yum yum yum....". This type of tart is also known as a crostata.