Ancho chilies are a type of dried chili pepper commonly used in Mexican and Southwestern U.S. cuisine. The pepper is the dried version of is the poblano pepper—to be specific, it’s the dried version of the ripe version of the poblano pepper.
In other words, the chilies we know as pobblano peppers are fresh chilies that are harvested before ripening, which is why they’re green. It’s what your basic “Chile Relleno” is made with. But when allowed to ripen, Poblanos turn red and develop additional sweetness, which in turn balances out their already mild heat. Thus Anchos are red while Poblanos are green.
Incidentally, the word ancho translates to “wide” in English, while poblano refers to the state of Puebla in central Mexico where the peppers are supposed to originate.
Ancho chilies can be reconstituted by soaking them in warm water, or they can be ground up or crushed and added to a recipe in that fashion. They have a deep red color and a wrinkled skin. Sweet and smoky with a flavor slightly reminiscent of raisins, their heat is mild to medium-hot.
You could also use a spice grinder to grind dried ancho chilies into a powder to use in spice rubs or for making mole, enchilada sauce, and chili.