The term "theory", even in its proper scientific context, has a wide variety in it meaning. Some theories, like the "theory of evolution", have lots of supporting evidence, and are widely believed to be true, or more accurately "to describe a model that represents the reality quite well". However, other theories are wildly conjectural, and seem quite unlikely to be true, and many have in fact been found not to be true. The main issue, as I see it, is that many NON-SCIENTISTS insist on making some sort of differentiation between theories and facts - with the idea that "theories are less certain" - which is untrue. And, in fact, many use it in a diminutive sense - as "only a theory". The reality is that virtually everything we think we know is teory - but some theories are much better supported by evidence, and have been found to more consistently describe reality, than others. The actual truth is that MOST of what we believe we know is a theory at one level or another. No human being has ever left our solar system... therefore EVERYTHING we "know" about astronomy is "just a theory". Everything we see outside our solar system could really be a really cool moving painting on the inside of a giant glass ball. I doubt it, and I'm quite certain that most of the theories we have about whats going on out there will turn out to be reasonably close to the reality, but for now it is all "just theories".