https://www.hsph.harvard.edu/nutritionsource/processed-foods...
And I quote:
"Ultra-processed foods
Also commonly referred to as “highly processed foods,” these are foods from the prior group that go beyond the incorporation of salt, sweeteners, or fat to include artificial colors and flavors and preservatives that promote shelf stability, preserve texture, and increase palatability. Several processing steps using multiple ingredients comprise the ultra-processed food. It is speculated that these foods are designed to specifically increase cravings so that people will overeat them and purchase more. They are typically ready-to-eat with minimal additional preparation. Not all but some of these foods tend to be low in fiber and nutrients. Examples are sugary drinks, cookies, some crackers, chips, and breakfast cereals, some frozen dinners, and luncheon meats. These foods may partially if not completely replace minimally processed foods in some people’s diets. One study using data from the U.S. National Health and Nutrition Examination Survey found that ultra-processed foods comprised about 60% of total calories in the U.S. diet. [4] An association has been suggested between the increasing sales of ultra-processed foods and the rise in obesity. [3]"
In short, ultra-processed food is food that's full of stuff you don't need to eat or you don't want to eat, but that's there to make you buy the product, and keep buying it. It's food whose purpose is not to nourish, but to sell.