Marrows are essentially giant zucchini. My mother makes a marrow and ginger preserve that is quite good (sort of like a gingery marmelade).
Squash: we don’t eat much of it. Pumpkins are usually only around the place at Hallowe’en, butternut pumpkin (or squash) is becoming more popular though. African or Caribbean shops usually have more varieties.
Pop corn is popcorn. You can buy microwave popcorn, kernels to pop at home in a pot or corn popper, and ready-popped stuff (Cheddar cheese flavour popcorn is popular in Ireland for some reason). It’s standard cinema food, in the UK either sweet or salty, in Ireland only salty popcorn is available in the cinemas.
During the potato famine Britain imported maize (then known as “Indian corn”) to feed the Irish. Unfortunately they didn’t know how to cook it or prepare it, and it wasn’t a successful venture.
Since my mother grew up in Zimbabwe she knows all about maize, but still can’t stomach polenta because of a bad experience with “sudza”/ “mealie meal” as a child. From what I can gather it involved a gecko falling into the pot one morning and my mother being served boiled lizard in maize porridge for breakfast.