Obiter dicta are remarks made from the bench or in written form by a judge that may form part of an opinion or judgment but are not in and of themselves legally significant; that is, the judgment or opinion they're included in would stand on its own without them. The term itself is Latin, the plural of obiter dictum, and is usually translated as “something said in passing.” Found in all but the briefest of judicial statements, these remarks are a routine part of jurisprudence worldwide.
When a judge issues a judgment, opinion or other statement, it's usually couched in prose, especially when it's a judgment or sentence, and consists of far more than a sentence or two laying out the judgment or sentence. Most judicial statements include one or more explanations of the decision, the judge's recitation of the facts of the case, interpretation of those facts, how courts in the past have dealt with those facts, and so on. They may also review and interpret the evidence presented, and explore its relation to the rest of the issues in the case. In many cases, they'll use other examples and analogies to express and explain themselves. These examples and analogies are all obiter dicta that may make it easier to understand the opinion without adding to it.
When a court has multiple members and a dissent is issued, the dissent itself also has the status of obiter dicta because it's a statement issued by the court that doesn't have official legal weight. Although they don't carry any legal weight in and of themselves, obiter dicta are sometimes cited in later opinions and decisions, whether they are identified as such or not.
While they don't carry official legal weight, obiter dicta can be influential. For instance, a judge, in imposing sentence, might point to specific elements of the crime or the convict's history that justifies a harsh or lenient sentence. These statements aren't generally necessary for the imposition of sentence, and are thus obiter dicta,, but will be thoroughly reviewed both by prosecutors and defense attorneys presenting cases before that judge in the future. Another example of the significance of obiter dicta is cases where courts decline to accept a case because of lack of jurisdiction. Having declined to rule on the merits, courts sometimes remark on the merits of the case. These remarks have no official standing but still significant as official utterances of the court.
Obiter dicta can be influential even in the absence of a real decision. US Supreme Court Justice Morrison Waite, in 1886, made some remarks prior to oral arguments in a case. His remarks were captured and included in the case's transcript, and have since become the bases for the legal doctrine that “juristic persons” — that is, non-human legal entities like corporations and partnerships — are entitled to the protections of the US Constitution's 14th Amendment.