Banana peppers are a particular variety of pepper from the species Capsicum annum, which also includes mild bell peppers and all types of spicy chili peppers. Banana peppers are thought to be native to Central America and Mexico. Early traders spread them throughout North America and back to Europe, where they became especially popular in Italy. The peppers are about six inches long and have a tapered shape resembling a banana. They are mainly picked and sold when they are slightly underripe and their waxy skin is bright yellow. The peppers turn a deep red when they are fully ripe. The crisp flesh contains minimal amounts of capsaicin and therefore is not spicy. Instead, it has a sweet and mild flavor.
Banana peppers are more difficult to find than bell peppers. Your best bet is probably a farmer's market during the summer. The peppers should be stored and used in the same way as bell peppers. They are often used raw in salads and sautéed for hot dishes. They can also be stuffed with grains or meats and baked. The peppers are also commonly pickled. They are full of nutrients like vitamins A and C and potassium.
Banana peppers are often confused with yellow wax peppers, also known as Hungarian Wax peppers. Both have a similar appearance but the latter are originally from Europe and very spicy in comparison. If possible, try to sample the peppers or ask the salesman to make sure you are getting the mild banana pepper.
cswiii adds:"you might further mention/reiterate that, no, those deli peppers you get at sub shops are _not_ banana peppers. I am thinking the subway peppers are yellow wax or hungarian wax peppers, which are closely related to banana peppers. banana peppers are not spicy at all, however, whereas
the deli peppers are, at least to an extent. Often the term is used interchangably, but doing such isn't fully correct.