These are the peppers that Italians have bred over the past few centuries to be sweet with just a bit of zing, perfect to go with Italian cooking. They grow about 3 inches (7.5 cm) long, and have wrinkled skin. They are either picked and used green, or let ripen to a slightly hotter red. They are often included as part of a pickled antipasto mixture. Some people might consider them "hot peppers", but they are actually still sweet peppers with just a bit of nip to them.
They are sold fresh, pickled or dried and flaked. There is some confusion as to whether "Pepperoncini" refers to them only when they are pickled, but the name in fact applies to the peppers in any state.
Heat level: 100 - 500 Scoville units.
Red Bell Peppers are too sweet and won't have enough zing. On the other end of the scale, Serrano Chile Peppers would be way too hot. You want a pepper somewhere in between the two. Banana Peppers, though way bigger, might do the trick if your recipe is going to have you chop them up anyway. But if a recipe calls for 1 Pepperoncino (the singular), then only use an equivalent amount of a bigger pepper.
The "c" towards the end is pronounced "ch".