A sandwich is, by definition, fillings sandwiched between two pieces of bread-like matter.

A hamburger is a sandwich, because it has fillings between two slices of a bread, whether it be a bun or a waffle or whatever. If the fillings are between something like other meat patties or is in a pita pocket or something, it ceases to be a sandwich, because the filling is not sandwiched between two slices of bread-like matter.

A hot dog is not a hamburger, which is a sandwich, because hamburgers require the use of a patty, a sauce, and pickles, where a hot dog does not. The pickles are the most important part of the burger, because the acidic taste counters the pungency of the meat and sauce. A hot dog needs no sauce or pickles to be eaten, nor is it a patty. Furthermore, it isn’t even a sandwich because it does not sit between two pieces of bread, but between one that’s folded in half. At best, it could be an open faced sandwich, which isn’t technically a sandwich, but a layman’s term for people who need a word for such a creation. If one attempts to separate the bun at the fold, it becomes a sandwich, but ceases to be a hotdog, as it is no longer served on a connected hot dog bun. It is simply a long, disappointing sandwich that has little flavor. Adding toppings such as a sauce or pickles would improve the taste, but it would not turn it into a hamburger, because the meat is still in the form of a log.

Also, if one were to eat a meat patty on a bun, with no sauce or pickles present, it is not a hamburger, but another disappointing sandwich, this time in the form of a round disappointment instead of a long one.

If one were to make the argument that a sub is a sandwich, they would be correct only if the bread has been completely separated. If it is still connected at a joint, it becomes a true sub, Jersey-style. It is not a hot dog because it is served with deli-cut lunch meats, not a log shaped bit of meat. If you make the sub hot, such as a meatball sub or a Philly cheesesteak, it ceases to be a sub entirely, and becomes the name after which it is called (i.e. Philly cheesesteak). If the hot sub is served on a baguette instead of a regular bread, it becomes a po’boy, such as those that are found in the Southern U.S.

Wraps and burritos are just that. They do not qualify as sandwiches even slightly. The same applies to tacos (hard and soft), shawarma, pita-wrapped kebab, anything in a crepe, or pizzas. Folding a pizza in half New York-style does not make it a sandwich. Quesadillas fall under the category of sandwich because there are fillings sandwiched between two tortillas.

Sandwiches made out of ice cream and cookies are sandwiches, simply sweet instead of savory. This applies to all other like products that pair a sweet filling between two sweet bread-like matters. Cake and pie, however, are not sandwiches, nor are any form of tart, blintz, or crepe. These have multiple layers, insufficient amounts of bread matter, or the lack of a second piece of bread matter, ruling them out from the sandwich category.

All forms of dumplings, no matter the culture, are not sandwiches, as the filling is simple stuffed into a wrapper folded in half.

Egg rolls, spring rolls, won tons, and other similar foods are also not sandwiches for the same reason.

If one were to take a slice of bread and sandwich it between two pieces of bread, they’d be that weird person that eats bread three slices of bread at a time. Bread cannot stand in as the filling for a sandwich.

Two slices of bread with nothing between them is not a sandwich, because there is no filling. That only makes you the weirdo who eats bread two slices at a time.

Furthermore, condiments cannot be used as fillings. A butter sandwich does not exist, nor do ketchup, relish, marinara, soy sauce, or any other similarly themed sandwich. Toast with jam is an open faced sandwich (not a sandwich), but if two pieces of toast with jam on them were pressed together, a sandwich would be created.

Having two pieces of toast with jam and stacking them so the jam ends up on the outside of one piece of bread does not make a sandwich, because the contents are not entirely inside the bread.

Muffins, bagels, crumpets, english muffins, and other similar foods that have been split in half with the intention of filling them with a designated filling creates a sandwich, as they are all bread matter. Pasta cannot serve as bread matter, because they are too small to accommodate any filling worthy of being called a sandwich. Lasagna is not a sandwich for the same reason cake is not a sandwich; there are too many layers.

I hope this clears things up for some people.

TL;DR: Don’t even get me started on how cereal isn’t a soup.