Banana peppers are called chiles güeros in many regions of Mexico. Güero, translates to blond, name given because of their pale, yellowish color. There are different varieties or banana peppers, but they are pale and light in looks, have waxy skin, and a similar flavor to Jalapeños. Their heat level can range from mild to hot (continue for more information and photo).
There is a variety of banana peppers different from the one in this photo, that is a bit more elongated in shape, which is very popular for pickling. Banana peppers are sold in many stores in the DC-MD-VA area, but if you are unable to find them, you can substitute with Jalapeños.