A burro is a burrito under a regional name. Across parts of Northern Mexico and into Arizona, the everyday word for the rolled flour-tortilla bundle is not burrito but burro, the unshortened animal name, and the diminutive burrito reads as the outside term. The build it describes is the same essential pairing every burrito depends on: a savory filling and a thin wheat tortilla that contains it. The filling supplies flavor and substance but no structure on its own, and the tortilla supplies a neutral, foldable wall but nothing to say without something inside it. The burro is simply that pairing as it is named where it is eaten, and the name carries a regional identity the food itself does not change.
What a well-made burro looks like is what a well-made burrito looks like, with a Northern accent. The tortilla is the Sonoran-style wheat round the region is known for: large, very thin, sometimes nearly translucent, warmed on a comal until it is supple enough to fold without cracking. The filling, often machaca, carne asada, beans, or chile colorado, is cooked down until it is tender but dry enough that it will not waterlog the wrap, because a wet filling is what turns a clean burro into a torn one. The filling is laid in a disciplined line down the center, the sides folded in, the cylinder rolled tight and closed at the ends so it eats evenly and stays sealed. The thin Sonoran tortilla is the regional signature: it is what lets a burro be rolled long and slim rather than thick and stubby, and a sloppy, overfilled version loses that elegance and splits at the first bite.
Stretch the same burro to an exaggerated length and you reach the burro percherón and the long Sonoran specialties, which deserve their own article rather than being crowded in here. Deep-fry it until the shell blisters and you have the chimichanga, structurally a different animal, which deserves its own article rather than being crowded in here. Use the related feminine term heard in some areas and you are talking about the burra, a parallel regional name with its own usage and its own thin-tortilla tradition, which deserves its own article rather than being crowded in here.