popcorn
Synonym discussion
Sense: noun/1
Popcorn is the normal general word for this snack. Popped corn is a more literal phrase, and learners will see it far less often in everyday English. Kettle corn and caramel corn are not full synonyms: both name specific sweet styles of popcorn, so they cannot replace popcorn in every context. If you ask for popcorn at a cinema, you mean the basic snack in general, not one special sweet type. A useful memory point is this: popcorn is the wide category, while kettle corn and caramel corn are narrower kinds inside that category. You can say, 'We bought popcorn before the film,' but 'We bought caramel corn before the film' only works if that exact sweet kind is meant.
Etymology
This word was formed in English from pop and corn. The first part refers to the sharp bursting sound made when the kernels open under heat, and the second part names maize. It first referred to the corn that opens this way and then to the snack itself. The later figurative uses compare light entertainment with easy snack food.