The question that ruins dinner parties
Ask a room full of friends whether a hot dog is a sandwich and you will lose at least one of them by morning. The argument is older than it looks. It predates the internet, predates the USDA classification, predates even the National Hot Dog and Sausage Council's 2015 declaration that a hot dog is, definitively, not a sandwich. (The council, it should be noted, has skin in the game.)
The trouble is that we have never agreed on what a sandwich actually is. Most people, asked to define one, fall back on something like "stuff between two pieces of bread." That definition collapses on contact. An open-faced sandwich has one piece of bread. A wrap has no slices at all. A club sandwich has three. A burger involves a bun split horizontally, is that one piece of bread or two? And what about ice cream sandwiches, which use cookies?
The definition we choose says more about how we think than what we eat.
The structural purist
The structural purist defines the sandwich by architecture. Two distinct slices of bread, separated by filling, eaten by hand. Under this rubric, a hot dog fails immediately, its bun is a single piece of bread, hinged at the bottom. A taco fails. A wrap fails. A burrito, obviously, fails.
This is the position of the State of Massachusetts, which in 2006 ruled in White City Shopping Center v. PR Restaurants that a burrito is not a sandwich. The case turned on a non-compete clause in a Panera lease that prohibited other tenants from selling sandwiches. A Qdoba opened in the same plaza. Panera sued. The judge sided with Qdoba, citing Webster's: a sandwich requires "two thin pieces of bread, usually buttered, with a thin layer (as of meat, cheese, or savory mixture) spread between them."
The purist position has the appeal of clarity. It draws a line and holds it. The trouble is that the line, drawn this way, excludes things almost everyone calls sandwiches. The Cubano is pressed into a single compressed object. The Vietnamese bánh mì uses a baguette with one continuous crust. The Italian panini is, by definition, pressed flat. By a strict structural reading, none of these are sandwiches either.
The ingredient rebel
The ingredient rebel takes the opposite view. A sandwich is defined by what it does, not what it looks like. It is bread (or bread-like substance) wrapping or supporting filling, designed to be eaten by hand. Under this rubric, a hot dog is a sandwich. A taco is a sandwich. A wrap is a sandwich. An Oreo is, technically, a sandwich (a cookie sandwich, at least). A Pop-Tart is arguably a calzone, which is arguably a sandwich.
This position has its champions. Merriam-Webster, in 2015, expanded its sandwich definition to include "one slice of bread covered with food," which would also pull in toast with peanut butter on it. The dictionary's job is to describe usage, not police it, and people do casually call all of these things sandwiches when it suits them.
The ingredient rebel position has the appeal of inclusion. It refuses to gatekeep. The trouble is that it eventually means everything is a sandwich, at which point the word means nothing. If a Pop-Tart is a sandwich, what isn't?
The Cube Rule, and other heresies
A few years ago, an internet diagram called the Cube Rule went viral. It proposed classifying all carb-based foods by where the starch is located on a cube. A taco (starch on the bottom and two sides) is a taco. A hot dog (starch on the bottom and two sides, hinged) is also a taco. A sandwich, the Cube Rule insists, must have starch on two opposite sides, top and bottom. Anything else is a different category entirely. Under the Cube Rule, a calzone is a calzone, a quesadilla is a quesadilla, and a sushi roll is, somehow, a sandwich.
The Cube Rule is a joke that takes itself half-seriously, which is the most dangerous kind of joke. People started applying it in earnest. They started using it to settle arguments. The diagram leaked into food blogs, into culinary school discussions, into the food editor of The New York Times writing a column about it. A joke about taxonomy became a working taxonomy.
What we actually mean
Here is the secret about the sandwich definition debate: nobody is actually trying to figure out what a sandwich is. They are trying to figure out what they think a sandwich is. The argument is a mirror. Some people want the world to be tidy and rule-bound, with clear categories and reliable membership. Other people want the world to be flexible and inclusive, with categories that bend to fit experience. Neither side is wrong. Both are doing taxonomy as identity work.
The truth, if there is one, is that sandwich is not a precise term. It is a family resemblance. Bread and filling, eaten by hand, in some configuration that suggests intentional construction. A hot dog is sandwich-adjacent. A taco is sandwich-adjacent. A wrap is sandwich-adjacent. Whether you let them into the family is a matter of how big you want the family reunion to be.
For the purposes of this encyclopedia, we are generous. We include the wrap, the bao, the open-faced smørrebrød, the pressed Cubano. We include things that argue their way in. We exclude the hot dog, but only because hot dogs already have their own encyclopedia. We will field your angry emails about this.
A sandwich is, at minimum, two things: bread (or something doing bread's job) and filling (or something doing filling's job). It is held in the hand. It is eaten without ceremony. It is the food you make when you do not want to think about food but still want to enjoy it. That is sandwich enough for us.