Tacos with pollo (chicken), chorizo (spicy sausage) and aguacate (avocado) need little explanation. The exotic-sounding offerings in the traditions of Guadalajara’s street-side stands may be less familiar. Use this glossary to know exactly what you’re getting.

Al pastor: Pork marinated with pineapple and as many as two dozen other ingredients, often vinegar, guajillo and ancho peppers, onion and oregano, until it’s sweet, sour and spicy. For Mexican chefs in search of the perfect taco, “the whale is al pastor,” says Troy Hickman of the under-construction Impala Cantina. “That’s the hardest one to pin down. People are really secretive about their recipes.”

Asada: Beef, typically skirt steak, cooked on a griddle and sliced into small pieces just before serving. It’s especially popular with American customers.

Lengua: Poached beef tongue. Ask Jesus Santacruz of Tacos El Chilango about them, and he sighs and shakes his head: “Es muy laboriosa” [very laborious], he says. Beef tongue is boiled with onion, garlic and a handful of other ingredients for at least three hours, then peeled of its outer skin, sliced and steamed. Then it’s usually served with salsa verde on top. “It’s actually very, very tender, once it’s cooked correctly,” says Joe Orozco of Mama Chuy, who suggests it’s more tender than chicken.

Tripas: Intestines. Tripas are generally boiled and then pan-fried until crisp. Their strong flavor may be why they’re not frequently served in D.C. taquerias.

Rajas: Pan-fried poblano peppers, which are milder than jalapenos but spicier than your standard bell pepper. They’re frequently served in vegetarian tacos, including those at El Chucho, Tacos El Chilango and Mama Chuy.