What can be classified as "fast food"?

My classmates and I just had a discussion for a task. We were discussing about fast food. One of the classmates claimed that instant noodles and canned food could also be classifies as fast food. She argued that fast food didn’t have to be limited to pizzas, hamburgers and the like, it could be anything that was fast to be prepared (or needed no preparation) and eaten. Well, that sounded a bit strange to me because I have never heard anyone saying that instant noodles and canned food are fast food before.

What do you think can be “fast food”? Can anything quick to be prepared and eaten considered fast food?