Pie crusts are a paste of fat and flour. They are very high in food energy. The fillings can be many things. Vegetables and meat-filled pies are for the main course of a meal. Dessert pies are filled with fruit or custard.
The origin of the word pie is uncertain. In my opinion it probably comes from the same source as the word pastry. It may have been an unrecorded Norman French word derived from the Old French pastoier, which is from the Latin pasteria. The word does come from the time when the Norman French ruled England. Originally in the late 12th century the word pie meant meat or fish wrapped in pastry. It was not until the 17th century that fruit pies were invented.
In British English fruit pies are usually covered with a pastry top. If they are uncovered they will usually be called a tart (from the Old French tarte) or a flan (from the Old French flaon). English words for food often come from French. In American English the word pie is used for a covered or uncovered fruit pie. There are a great many popular fruit pies. The filling is fruit, sprinkled with a little sugar, spices or other flavourings.
Other pie top covers can include a meringue made of beaten egg whites. Cream pies have a cover of whipped cream over a custard stuffing.1
Pumpkin pies are filled with pumpkin custard. They are from North America and are the traditional Thanksgiving dinner dessert.2
Lemon and vinegar pies are also popular in North America.3
The word pie is used in many idioms. Something easy to do is described as easy as (eating) pie. To eat humble pie originally meant to eat 'umbles' meaning the cheap organ meats of deer or other animals. This meaning is no longer used, but the phrase to eat humble pie survives as an idiom for apologising and being humiliated. To have one's finger in a pie is an idiom for being involved with a business, possibly taking a corrupt share.
Pies are an important part of English culture, with a long history. They are the main course of the meal and the dessert. They also represent key cultural ideas.
1. In England the word custard usually refers to a sauce of this type poured over a dessert.
2. Thanksgiving is a harvest festival to give thanks for a good year. The dates have varied. It is currently celebrated on the 3rd Monday in October in Canada. The warmer United States has a later harvest and celebrates it on the fourth Thursday in November.