At the beginning of "An Introduction to Rhetoric", Foss, Foss, and Trapp define rhetoric as being "bombastic words with no substance or trivial talk". To my very limited understanding, this definition carries with it very negative connotations, which I don't automatically think of when considering the word rhetoric itself. Thankfully enough, though, Foss et. al. go on to say that "rhetoric should not engender only negative connotations", but the opposite in that it has quite "a distinguished history of large positive meanings". Moving even further, the author's say that their definition of rhetoric "features the use of symbols by humans". I, however, am not that sure that I completely agree with either of these definitions. I certainly don't think that the "no substance" definition is correct, considering how much we use rhetoric in our day to day lives and how without it, we wouldn't be able to communicate. But, much deeper than that, I believe that rhetoric is not only our ability to communicate, but the very specific way in which we do it. For instance, what if I said "Hey, yo! Muhlhauser! Come gimme sum help wit dis stuff". Well speaking in this sort of slang would probably not invoke the same type of response as it would if I were to instead say "Excuse me, Doctor Muhlhauser. I need some help with this please".
          That being said, here are two definitions of the word rhetoric that I think are correct.
1. Rhetoric: The art or science of all specialized literary uses of language in prose or verse, including the figures of speech.
2. Rhetoric: (In Classical Oratory) The art of influencing the thought and the conduct of an audience.

Both definitions came from Dictionary.com. (URL  http://dictionary.reference.com/browse/rhetoric)