I have often received questions on the subject of flautas and taquitos (also called tacos dorados)—mainly about how to tell them apart and what makes them different. As with so many Mexican cuisine-related topics, there is a short answer and a longer, much more nuanced and complete one.
Flautas and taquitos are very similar and the terms are used interchangeably depending on geographical location and personal preference.
More comprehensive discussion:
Taquitos and flautas are sometimes categorized by their size, shape, or the particular kind of tortilla used in their preparation.
Oftentimes the term flautas (which translates as “flutes”) is used to refer to a large flour tortilla that is rolled up around a filling and deep fried. Sometimes these are rolled to be narrower on one end than the other to create a long, tapered cone shape. When this criterion is used, the other term, taquito (literally, “little taco”), refers to a corn tortilla rolled in a similar fashion with a filling of beef, chicken or cheese, then fried until crisp.
Other times, the crucial difference is found in the length. In some areas of Mexico, a flauta is very long and thin, made from a burrito-sized flour tortilla or similarly-sized corn one. Taquitos, on the other hand, are the shorter versions, rolled from regularly-sized corn or flour tortillas—or even from small appetizer-sized ones if the taquitos are intended as a snack or first course, rather than as an entree.
For some Mexicans, the shape of the rolled tortilla is the determining factor: flautas are carefully rolled to be round (and cooked in abundant oil in order to keep that shape), while taquitos or tacos dorados use a twice-folded tortilla rather than a rolled one, making for a somewhat flattened product that can easily be fried in much less oil.
To further complicate matters, many street food stands in central and southern Mexico sell a very similar item (usually a corn tortilla folded around a filling) and call it a fried quesadilla—even when (as happens in the Mexico City area) it does not contain cheese! Quesadillas, however, are usually not fried for as long as are flautas/taquitos, resulting in a much less crunchy product.
In any case, flautas and/or taquitos are usually served topped with or on a bed of chopped lettuce or cabbage, sometimes accompanied by diced tomatoes, onions, and/or avocados. They are often adorned with shredded or crumbled cheese and crema or sour cream, and offered with a choice between two or more sauces (often a red one and green one) as a condiment. Guacamole and/or refried beans are also frequently included as part of a serving of taquitos or flautas.