I happen to think it could also be defined as food that reminds you of your childhood.
For me, it's this:
Buttery noodles drenched in parmesan cheese.
It's what I used to eat all the time at home as a kid on the weekends when my parents were out of town (except back then, I loaded it up with squeeze butter, not the real stuff. Gross.)
It's what I ate the other day after a long day at school. It's just what sounded good - this time with gluten-free noodles, of course, and way too much parmesan cheese.
What's a favorite comfort food of yours?