An opinion is very similar to an anal pore in that pretty much everyone has one, but they all stink.
 Fact vs Opinion
An opinion differs from fact in that everyone, no matter where they are, can view facts but opinions are a matter of the interpretation of fact. The wavelength of light coming from a light bulb is fact but the fact that it is too bright, too dim or even what colour it is, is opinion.
It is common for people to confuse fact and opinion, as anyone who has done English (or insert your own native language) at school and asked to review something will know. Dressing up opinion as fact is a tactic used to coerce people into a particular way of thinking. For example; the phrase "the film is crap" is an opinion, but worded as fact, "I think the film is crap" is better as it makes it clear that it's opinion. "I think the film is crap because..." is even better, but slightly off topic. Whether movie critics will ever learn this is unknown. "Fact" is generally treated as being a higher category than "opinion", but opinion can be a perfectly valid basis for subjective decisions. For instance, suppose Person One asks "Why don't you want to watch this movie?" and Person Two says "Because it's crap". If Person One then replies "That's just your opinion", then Person One may be missing Person Two's point about their emotional reaction to the filk.
Rewording an opinion into a statement about that opinion can turn the statement into a fact, albeit one on a different topic; saying "I think this movie is crap" is technically speaking a fact, but is mot a factual statement of the film's quality, but merely of one's impression of it. Similarly, facts can be dressed down as opinion; creationists and intelligent design proponents will often equivocate that evolution is "only a theory". In this case, they jump on the misconception about what a theory is in order to dismiss it as "merely opinion".
Some people consider the controversy and conflicts as "opinion" and that there are no objectively true statements: the mere fact that people disagree taken as evidence that it is merely "opinion" when any opinion, when evaluated objectively, may prove to be based in fact and thus would be the more reasonable option to follow. Or it could be a web of lies built on a throne of deciet. Until careful testing, either is possible.
 Fact vs. Statement of Fact
The term "statement of fact" is often used to refer to any statement that asserts something that, if true, would be a fact. Thus, something can be false and still be a statement of fact, if it's dealing with factual issues. Examples:
"Life appears to be designed": opinion
"Life was created less than six thousand years ago": statement of fact
"The scientific consensus is that life is billions of years old": fact
Some say that truth in religion is simply the opinion which survived. It's certainly true that opinions (such as geocentrism) don't tend to last very long after they are found to blatantly contradict established facts. We'll just have to wait on creationism.
 See also
- Scientific method - What distinguishes fact and opinion. And more specifically, good opinion from bad opinion.
- Theory - Of the scientific kind, when opinion is so close to fact that people get very edgy indeed.
- Fact - [citation NOT needed]
- Pommer's Law - What happens to people's opinions on the internet.