@jerv gave a very good response. (There’s nothing wrong with @dabbler‘s explanation, either.)
I don’t know of any – any! – “proven facts” in science, because even the observations that are made “as proven fact” to support or declaim one theory or another are themselves subject to revision because of “better observation” or better experimental setup that refines or sometimes even contradicts the original observation.
A scientific theory is “the best explanation of ‘reasons why’ things are the way they are or act as they do”, and every theory is subject to revision when observations are made that don’t fit the theory (and the observations are verifiable and “true” to the best of anyone’s knowledge, and repeatable, as @jerv was correct to note).
@Rarebear is also very close to correct in his statement that “in colloquial terms” and to lay people who don’t do research and experimentation of their own, or don’t follow the fine details of others’ scientific research, a theory is “an accepted fact” (in contradistinction to a “proven” fact). For example, we accept atomic theory as factual because the careful observations that have been made in attempting to disprove it – which is the way science works, after all – have failed to do that. The models work, the theory is valid “as far as we know”, and those of us who don’t do pure research can rely upon the “accepted facts” about atoms, their makeup of electrons, protons and neutrons, and expect that the world is built that way. At least until we start to gain a better understanding of quantum mechanics and realize that there are huge holes in “atomic theory”, so all the things that we thought we knew years ago, and accepted as true, are no longer at all certain or even true.