"Processed food" is food that's been prepared in some complicated way before being sold to customers. Examples include:

• crackers
• canned soup
• snack bars
• candy
• frozen dinners

People think of processed food as being unhealthy. If you want to talk about this kind of food in a more positive way, you can call it "prepared food".

The word "food" is usually uncountable. However, if you're talking about a variety of different kinds of food that you don't eat all at one time, you can call them "foods". So you say:

I ate so much food!

But you can say:

A healthy diet consists of a wide variety of different foods.