Hot Dog

I have been having problem with the phrase "hot dog". Throughout my whole life, hot dog has been referring to a sausage and a soft roll (two together as a whole). However, since my arrival into the US, people here in the United States has been referring to the sausage as hot dog. Then, what exactly is the definition of a hot dog?? According to the American Heritage Dictionary, hot dog is "A frankfurter, especially one served hot in a long soft roll" (www.bartleby.com). So, does it mean a beef/pork sausage is called a hot dog when it is served in a soft roll?? Another question also arises with the hot dog-equal-sausage definition. If hot dog is only referring to the sausage, then why do you get a soft roll when you order a hot dog??

I think the usage of English words is really interesting. In some cases, the usage of one word is altered, in which the meaning of a word is also altered. I just like to make things clear.

Words that are funny to me:
jelly = jello??
bandage = bandaid??