"Three things cannot be long hidden. The Sun, the moon and the truth."
A FACT is something that has really occurred or is actually the case. The usual test for a statement of fact is verifiability, that is whether it can be proven to correspond to experience.
An opinion is a judgment, viewpoint, or statement about matters commonly considered to be subjective, i.e. based on that which is less than absolutely certain, and is the result of emotion or interpretation of facts.
*See Wikipedia for more on Fact, Truth and Opinion.