A burrito is a Mexican dish originating in either Northern Mexico or the Southwestern United States according to The Food Timeline (http://www.gti.net/mocolib1/kid/foodmexican.html#burritos). Peter Fox wrote about his search for the origins of the burrito (http://www.randomwalks.com/poker/burrito.txt), placing the origin in Sonora. The type of burrito eaten in the US appears to be an indigenous variation, and is not common in Mexico. Different cities also have variations on the Mexican/American burrito.

It consists of a soft flour tortilla, typically filled with beans or meat, usually ground beef or carne asada (grilled marinated beef, minced), and rolled up so the filling is enclosed inside the tortilla. Other common meats are shredded beef, pork al pastor, carnitas (pork fried in lard), chicken, fish, shrimp, or sometimes exotic meats like tongue, brains, tripes, chicharrones (fried pork rinds stewed), and other ingredients often included are salsa, refried beans, whole pinto beans; Mexican rice; shredded lettuce or cabbage; diced tomato; sour cream; guacamole and shredded cheese.

A variation called the breakfast burrito consists of a flour tortilla filled with scrambled eggs, cheese, bacon, and salsa.

Burritos are common mainly in the cuisine of Northern Mexico. They are called tacos de harina (="wheat tacos") as you approach the east coast, and burritas (feminine, with 'a') in Northern-style restaurants outside Northern Mexico. In Mexican-American cuisine, crispy fried burritos with just one or two ingredients in the filling are called chimichangas, and a similar kind of burrito that's long and thin is prepared in Sonora and vicinity is called a chivichanga.

The name burrito comes from the Spanish diminutive of burro.

Source: Bayless, Rick and Deann Groen Bayless, Authentic Mexican: Regional Cooking from the Heart of Mexico (1987) (ISBN 0688043941), p. 142.