During an argument on line, I stated my thoughts on a subject. The reply went something like:
Them: Who asked you?
Me: I am entitled to have an opinion.
Then: Where is your evidence to back it up?
Me: Opinion - Noun - A belief or conclusion held with confidence but not substantiated by positive knowledge or proof.
A fact is a fact, whether or not anyone can prove it or knows it. (e.g. my grandmother died without telling anyone where she had hidden her will. It location is an unknown fact.)
An informed opinion might be a subjective one, and not a matter of fact at all. (e.g. I think that Tolstoy is a better novelist than Dickens. I am immensely erudite, have read everything that both of them ever wrote, have read every critic who has ever written on these authors - yet my opinion, though informed, is only an opinion, not a fact.