Peppers of any kind, bell or corni (horn-shaped). Italians especially like them roasted and put up sott' olio or sott' aceto as an antipasti. Peperoni ripieni, or imbottiti, or al forno will be stuffed; gratinati are stuffed too, then rolled in breadcrumbs and baked.
Hot peppers or chilies are peperoncini.
Americans accustomed to ordering a pepperoni pizza may get a pile of peppers instead of their beloved spicy little salame—this was invented by Italian-Americans in the early 20th century,and still hasn't made it back over the Atlantic. Perhaps the nearest equivalent is salsiccia Napoletana piccante.
Four peppers are in the Ark of Taste:
peperone corno di bue di Carmagnola: long yellow and red sweet peppers from Carmagnola in Piedmont; popular grilled, fried in olive oil or with a bagna cauda.
peperone di Capriglio: another Piedmontese pepper, small round and red or yellow, produced in the hills of Capriglio d’Asti.
peperone di Senise: from Basilicata, these are reminiscent of the Basque piments d'Espelette. Long and red, they are either consumed fresh or strung up in the sun to dry, then baked and turned into a powder with hints of saffron.
peperone quadrato della Motta: fragrant red or yellow squarish pepper grown in Motto, near Costigliole d'Asti. Also good in a bagna cauda.