Unpublished opinion refers to an opinion that the court has specifically designated as not for publication. These types of cases are not available for citation as precedent because the judges making the opinion deem the case as "less important". They are considered binding only on the parties to the particular case in which it is issued. These are state specific court rules prohibiting citing of an unpublished opinion as authority.
The following is an example of a State Court Rule (California) on Citation of unpublished opinion:
Cal Rules of Court, Rule 8.1115 Citation of opinions
(a) Unpublished opinion Except as provided in (b), an opinion of a California Court of Appeal or superior court appellate division that is not certified for publication or ordered published must not be cited or relied on by a court or a party in any other action.
(b) Exceptions An unpublished opinion may be cited or relied on:
(1) When the opinion is relevant under the doctrines of law of the case, res judicata, or collateral estoppel; or
(2) When the opinion is relevant to a criminal or disciplinary action because it states reasons for a decision affecting the same defendant or respondent in another such action.
(Subd (b) amended effective January 1, 2007.)
(c) Citation procedure A copy of an opinion citable under (b) or of a cited opinion of any court that is available only in a computer-based source of decisional law must be furnished to the court and all parties by attaching it to the document in which it is cited or, if the citation will be made orally, by letter within a reasonable time in advance of citation.
(d) When a published opinion may be cited A published California opinion may be cited or relied on as soon as it is certified for publication or ordered published.