While I never really understood the term, I always interpreted a "popcorn" film as like an insanely fun summer blockbuster hit.
I never really eat popcorn when watching movies, so I technically don't have one. The last time that I watched a film and ate popcorn at the same time was during Hitman on Blu-ray a few months ago. It was the first time I had popcorn in a good couple years.