Opinion
Opinion is a person's ideas and thoughts towards something. It is an assessment, judgement or evaluation of something.
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.
In judicial practice
In the US judiciary, opinion is the word used for a higher court's published decision which establishes new legal precedent, or supersedes or reverses existing precedent. Cases decided by the US Supreme Court, for example, sometimes become well-known because they express the court's "opinion" on how federal law (or the Constitution) is to be interpreted, which can have very wide implications (e.g. Roe v. Wade). This usage of the word opinion is different from the common usage (outside the legal field), because the court's opinion is not the opinion of any person, but the court's decision after careful deliberation of the case, and is binding on relevant future cases in lower courts. Other appeals courts, such as state appeals courts, also file opinions which serve the same function at the state level. An opinion can also be published at the insistence of a dissenting judge on the case.
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 decision 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 decision 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.