It seems ‘an intuition’ to what processed is to most people; some things are obvious ($1 per 12 freezer pack of burgers are not going to be unprocessed), but it gets less obvious fast…
Personally I consider a can of skipjack tuna in spring water to be unprocessed, even though it has been canned.
I consider a frozen bag of peeled and cooked shrimp to be unprocessed, even though it has been peeled, cooked, and frozen.
But a frozen bag of peeled garlic shrimp I would consider to be processed, because the ingredient list contains items I don't exactly know what they are.
So that's my definition, it's the ingredient list.