An opinion is a judgment, viewpoint, or statement that is not conclusive, rather than facts, which are true statements.
A given opinion may deal with subjective matters in which there is no conclusive finding, or it may deal with facts which are sought to be disputed by the logical fallacy that one is entitled to their opinions.
Distinguishing fact from opinion is that facts are verifiable, i.e. can be agreed to by the consensus of experts. An example is: "United States of America was involved in the Vietnam War," versus "United States of America was right to get involved in the Vietnam War". An opinion may be supported by facts and principles, in which case it becomes an argument.
Different people may draw opposing conclusions (opinions) even if they agree on the same set of facts. Opinions rarely change without new arguments being presented. It can be reasoned that one opinion is better supported by the facts than another, by analyzing the supporting arguments.[1]
In casual use, the term opinion may be the result of a person's perspective, understanding, particular feelings, beliefs, and desires.
Though not hard fact, collective opinions or professional opinions are defined as meeting a higher standard to substantiate the opinion.