Etymology
According to the Real Academia Española, publisher of Diccionario de la Lengua Española, the word taco describes a typical Mexican dish of a maize tortilla folded around food ("Tortilla de maíz enrollada con algún alimento dentro, típica de México"). The original sense of the word is of a "plug" or "wad" used to fill a hole ("Pedazo de madera, metal u otra materia, corto y grueso, que se encaja en algún hueco").[1] The Online Etymological Dictionary defines taco as a "tortilla filled with spiced meat" and describes its etymology as derived from Mexican Spanish, "light lunch", literally, "plug, wadding".[2] The sense development from "plug" may have taken place among Mexican silver miners, who used explosive charges in plug form consisting of a paper wrapper and gunpowder filling.[3]

History
The taco predates the arrival of Europeans in Mexico. There is anthropological evidence that the indigenous people living in the lake region of the Valley of Mexico traditionally ate tacos filled with small fish. Writing at the time of the Spanish conquistadors, Bernal Díaz del Castillo documented the first taco feast enjoyed by Europeans, a meal which Hernán Cortés arranged for his captains in Coyoacán.[4][5] It is not clear why the Spanish used their word, "taco", to describe this indigenous food.

Traditional tacos
There are many traditional varieties of tacos:

Tacos al pastor made with adobada meat.
Tacos Al pastor/De Adobada ("shepherd style") are made of thin pork steaks seasoned with adobo seasoning, then skewered and overlapped on one another on a vertical rotisserie cooked and flame-broiled as it spins.[6][7]
Tacos de Asador ("spit" or "grill" tacos) may be composed of any of the following: carne asada tacos; tacos de tripita ("tripe tacos"), grilled until crisp; and, chorizo asado (traditional Spanish style sausage). Each type is served on two overlapped small tortillas and sometimes garnished with guacamole, salsa, onions, and cilantro (coriander). Also prepared on the grill is a sandwiched taco called mulita ("little mule") made with meat served between two tortillas and garnished with Oaxaca style cheese. "Mulita" is used to describe these types of sandwiched tacos in the Northern States of Mexico, while they are known as Gringa in the Mexican south and are prepared using wheat flour tortillas. Tacos may also be served with salsa.[6][7]
Tacos de Cabeza or head tacos, in which there is a flat punctured metal plate from which steam emerges to cook the head of the cow. These include: Cabeza, a serving of the muscles of the head; Sesos ("brains"); Lengua ("tongue"); Cachete ("cheeks"); Trompa ("lips"); and, Ojo ("eye"). Tortillas for these tacos are warmed on the same steaming plate for a different consistency. These tacos are typically served in pairs, and also include salsa, onion and cilantro (coriander) with occasional use of guacamole.[6][7]
Tacos de camarones ("shrimp tacos") also originated in Baja California in Mexico. Grilled or fried shrimp are used, usually with the same accompaniments as fish tacos: lettuce or cabbage, pico de gallo, avocado and a sour cream or citrus/mayonnaise sauce, all placed on top of a corn or flour tortilla.[6][7][8]
Tacos de Cazo for which a metal bowl filled with lard is typically used as a deep-fryer. Meats for these types of tacos typically include: Tripa ("tripe", usually from a pig instead of a cow); Suadero (tender beef cuts), Carnitas and Buche (Literally, "crop", as in bird's crop; here, it is fried pig's esophagus.[9])[6][7]
Tacos de lengua, beef tongue tacos.[10] Cooked in water with onions, garlic, and bay leaves, for several hours until tender and soft, then sliced and browned through saute in a small amount of oil. "It is said that unless a taqueria offers tacos de lengua, it is not a real taqueria.[11]

Two fish tacos in Bonita, California
Tacos de pescado ("fish tacos") originated in Baja California in Mexico, where they consist of grilled or fried fish, lettuce or cabbage, pico de gallo, and a sour cream or citrus/mayonnaise sauce, all placed on top of a corn or flour tortilla. In the United States, they were first popularized by the Rubio's fast-food chain, and remain most popular in California, Colorado, and Washington. In California, they are often found at street vendors, and a regional variation is to serve them with cabbage and coleslaw dressing on top.[6][7]
Tacos dorados (fried tacos, literally, "golden tacos") called flautas ("flute", because of the shape), or taquitos, for which the tortillas are filled with pre-cooked shredded chicken, beef or barbacoa, rolled into an elongated cylinder and deep-fried until crisp. They are sometimes cooked in a microwave oven or broiled.[6][7]
Tacos sudados ("sweaty tacos") are made by filling soft tortillas with a spicy meat mixture, then placing them in a basket covered with cloth. The covering keeps the tacos warm and traps steam ("sweat") which softens them.[6][12]
As an accompaniment to tacos, many taco stands will serve whole or sliced red radishes, lime slices, salt, pickled or grilled chilis (hot peppers), and occasionally cucumber slices, or grilled cambray onions.