What is Traditional Food? (Thanks Abigail C for this question)
I have heard traditional food defined a number of different ways, but one fairly common idea is that traditional food is the food your great, great, grandmother would have cooked.
In the question, two seemingly opposite extremes were mentioned: the great ethnic cuisine, and Pizza. As it happens, both could be considered ”traditional”. The Nourishing Traditions cookbook (my reference for traditional foods) has a recipe for
Pizza on page 523, as well as many recipes with a more ethnic flair. I think the big distinction between traditional food and the deplorable modern junk, has to do with the amount of processing/purification food undergoes before it is eaten. The core idea is that traditionally, people ate a lot more whole food, like un-refined flour (whole wheat), instead of using a pre-made box of food, like mac and cheese. But, one could make mac and cheese out of ingredients that have not been heavily processed, which would be a traditional food. So then it’s the ingredients that matter, much more so than the dish being made. Also in traditional cooking there are a variety of kitchen techniques, such as soaking grain before making flour, which have been discarded by most modern food manufacturing. These techniques are considered integral to traditional food preparation. Frequently the terms “traditional food” and “slow cooking” are used interchangeably. Traditional cooking seeks to avoid shortcuts of modern preparation, and thus tends to take a much longer time.

One of the great ironies, as the traditional food movement gains popularity, is that you can now buy fully packaged “traditionally prepared” food. The legitimacy of these foods comes from the fact that people have preserved food for ages, but it does muddy the water as far as defining “traditional food” as “that which does not come from a factory”.
Some definitions of what makes up traditional fare (here I borrowed heavily from a list by Stephanie @ Keeper of the Home):
Grassfed/free range animals are traditionally raised, and all animal products in traditional cooking should come from these animals
Sugar is not refined from corn or sugar-cane (un-refined sugar from these plants may be ok)
Grain is fermented in some way before eating (for instance sour-dough bread)
Fats (including cooking oil) come from sources like animal fats, butter, palm oil and un-refined coconut oil… these kinds of oils and fats have a natural balance of fatty acids
Nuts that have been soaked
Sea salt (preferable from a non-polluted source, such as the Himalayas)
So, traditional foods really are the kinds of things your great, great, grandmother would have made. They are foods that have a long cultural history, like many ethnic foods. Some people have also determined a set of food handling practises that are common to numerous ancient cultures, and these are considered traditional cooking methods.
I hope this helps clarify what traditional cooking is!
-SN