If one looks up the word "theory" in Webster's dictionary it will read thus: "supposition put forth to explain something; speculation; exposition of general principles as distinct from practice and execution; (Colloq.) general idea; notion.
Now, supposition, speculation and notion certainly explains that "theory" is in essence hypothesis based upon what information is available. For example, the "Theory of Evolution" is based upon scientific findings and is an idea or notion as to how it works, but cannot be proven. Any other concept of the word "theory" itself as being "fact" one would have to re-write the english language in order to accommodate. Theories can be based on fact, but are not facts themselves until they are proven and then graduate into scientific law (like Newton's Law of Gravity).
Gravity is proven to exist and admitted in the scientific community, granted how gravity works is a theory because it is not known nor proven, hence the "understanding" of gravity being "theory." This is an excellent example of how evolution is a concept, and not the unrefutable explanation of mankind's origin. You certainly don't discredit gravity in such a statement, but the theory of gravity (and its theory-classified cousin, evolution) is indeed not fully understood nor proven.