Think about the definition of processed:
2 a : to subject to a special process or treatment (as in the course of manufacture)
To wit, any natural, whole food that has been put through some "treatment" fits the definition of processed.
As a very general rule, anything that's packaged in a can, box, foil or bag has been processed in some way. Anything that includes ingredients like monosodium gluta-whatever or polyhydrogenated sucra-something. Anything that needs a preservative to enhance shelf life. Even canned tuna, which I eat daily, is processed.
For me, it's just a matter of keeping the chemicals and preservatives to a minimum.