This jokey, pseudo-philosophical question exemplifies a confusion which lies at the heart of philosophy.

There are two ways to approach the question. One is to consult everyday usage: hotdogs are not commonly called sandwiches, and so therefore hotdogs are not sandwiches.

However, this feels too ad-hoc to philosophy types, who naturally take the second approach. First, define what a sandwich is. Then, determine if this definition is inclusive of hotdogs. The point of contention is how exactly to define a sandwich, since once a definition is arrived at, applying it to hotdogs is easy. As a first stab, you might define a sandwich as any or all of meat, cheese, and vegetables between two pieces of bread. But then, someone might counter, subs are called sub sandwiches, and they use one piece of bread. So then, sandwiches are meat, cheese, and/or vegetables wrapped in bread. But following complaints from the burritos-and-wraps-are-not-sandwiches crowed. you might amend to meat, cheese, and/or vegetables partially wrapped in bread. With this definition in hand, you can soundly conclude that hotdogs, contrary to popular opinion, are in fact sandwiches.

While this second approach might feel more logical and rigorous, this whole procedure is wrong. The problem is that the argument consults usage to arrive at a definition, then uses the definition to arrive at a conclusion contrary to usage. This cannot be legitimately done, because usage is the only source which informs you what a sandwich is. There is no trans-linguistic reality, no platonic essence of sandwiches which you can consult. Definitions can only describe, not prescribe, and you can't get more out of them than the usage they arise from. If your definition of sandwich is contrary to usage, then it is, by definition, wrong.

Nouns pick out categories. There is always at least some logic to them, if the same noun haphazardly selected sandwiches, deserts which go well with coffee, and baseball cards, it wouldn't be of much use. But, words are under no obligation whatsoever to have strict, logically consistent definitions. There may be no definition which perfectly includes and excludes every member of "sandwich", or of there is one, no one is thinking of it as they use the word. Words are organic things, and have fuzzy boundaries, and our minds are well constituted to deal with them as such. We happily use the word sandwich, never mistakenly using the word with hotdogs.

I call such questions which presume an trans-linguistic reality where there is none, "hotdog questions". I think this confusion pervades philosophy. Whenever a "what is" question is asked, I am always worried by the thought "Is this a hotdog question?". "What is identity?" may be one.