For example, one may claim that Strawberry is a better tasting flavor of Ice cream than Vanilla. Another might claim that vanilla is a better tasting flavor. (If you disagree with either of these opinions, substitute Chocolate, butter pecan, or whichever flavor of ice cream you think tastes better than vanilla, for my use of strawberry.) The original claim is an opinion; it is neither true nor false, it is simply a claim which can neither be proven nor disproven. Now, if one claims that strawberry is a more popular flavor than vanilla, that is no longer an opinion, it is a fact, which can be proven, (or in this case disproven) by showing another fact, that more vanilla ice cream is sold than strawberry. (The presumption being that people buy ice cream in order to consume it, thus, more purchases of vanilla would indicate vanilla is more popular than strawberry since people would not purchase ice cream simply to throw it away.)
The issue of whether strawberry ice cream tastes better than vanilla ice cream is still, however, Arbitrary and nonprovable, and thus remains an opinion (as would the opposite opinion that vanilla ice cream tastes better than strawberry. Note that simply because a particular opinion is more popular still does not make the opposite opinion incorrect or wrong). It would not be permissible for someone else to claim that either opinion on which tastes better is wrong because opinions are still arbitrary and can neither be proven nor disproven. It is permissible to state that one dh the opinion. It is, however permissible to claim that the statement that strawberry is more popular than vanilla is wrong, because it is a claim of a fact, the claim having been contradicted by one or more other facts.
Opinions can either be made up by a person or taken over from another person. Sometimes some people try to force their opinions on others. In general, all people are free to form opinions as they see fit. However, in certain political regimes, it may not be advisable to express certain opinions openly. In Economics, Philosophy, or other social sciences, analysis based on opinions is referred to as Normative analysis (what ought to be), as opposed to Positive analysis, which is based on observation (what is). Not all schools of thought find this distinction useful.
Not every case decided by a higher court results in the publication of an opinion; in fact most do not, since an opinion is usually only published when the Law is being interpreted in a novel way, or the case is a high-profile matter of general public interest and the court wishes to make the details of its ruling public. In the majority of cases, the judges issue what is called a Memorandum opinion instead, which simply points out how state or federal law applies to the case and affirms or reverses the decision of the lower court. A memorandum opinion does not establish legal precedent or re-interpret the law, and cannot be invoked in subsequent cases to justify a ruling. Opinions, on the other hand, always establish a particular legal interpretation. It is important to remember that, in the United States, a state appeals court does not re-evaluate the facts of the case, but is called on (according to the appellant's specific reason for appeal) to decide whether the law was applied correctly, or if there were errors in the Trial process that invalidate the Verdict or entitle the plaintiff or defendant to a new trial.