Well, Thanksgiving Day in the USA is a secular holiday (with some generic religious themes of appreciating our blessings) celebrating the arrival & survival of the first Puritan settlers (English Protestants) to the New England area of the North American continent in the 17th century. By extension, it celebrates all early settlers who came to what became the USA. Canada also celebrates a Thanksgiving holiday, in October rather than November. Thanksgiving Day is sort of a mix of harvest festival, a salute to the early European settlers, & a time to connect with family & friends (whether in person over a huge feast or by long-distance communications of telephone, email, etc.) It has also more & more over the years come to signify the beginning of the Christmas shopping season. And, of course, the men love to watch football matches (American style) on this day!
The meal is very important & the generic holiday meal is usually considered to be roasted turkey with some kind of highly seasoned bread-based stuffing/dressing (or other carbohydrate base such as rice), also some kind of sweet-potato dish, some variety of cranberry sauce or compote, & various pies for dessert. Of course, there are various vegetable accompaniments to the meal. Each area of the country has its own variation on the preferred foods for the meal, & the feast will incorporate the favored specialties of the area (seafood in coastal areas, fowl, beef, pork, or game in others). Turkey is almost de rigueur in addition to any other meat dishes. Pies tend to be the favored dessert with pumpkin (or other winter squash or sweet potato), pecan, & apple pies very common. It seems that eating until one is about to burst is the main focus!
It is a wonderful blend of traditions enriched over the years by all the immigrant cultures that have mixed into the mainstream American experience. And although it was only my husband & me here yesterday, we had a traditional kind of meal (only no turkey-- chicken breasts browned in butter then baked in a casserole over a bread stuffing; baked & mashed sweet potatoes with brown sugar, butter & spices; a freshly cooked cranberry sauce; & steamed broccoli-- we skipped having pie because we are already too big!). And we called all family members to visit & ask details of each others' meals. And hubby did indeed watch football! And then today we used up all the leftovers.