Obiter dictum (also obiter dicta, and often just "obiter"), from the Latin for "said in passing" is the legal term used to describe a discussion of a point of law in a judicial decision that does not directly relate to the point on which the court actually decided the case (the ratio decidendi). Under the principle of stare decisis, obiter is not binding on other courts, although it can be persuasive.
For example, in the key Supreme Court of the United States case Marbury v. Madison, the case was decided in Madison's favor when the court ruled that it had no jurisdiction over the dispute as the legislation that gave the court jurisdiction was unconstitutional. However, most of the decision discussed why if the court did have jurisdiction, it would have ruled in Marbury's favor. That section was obiter.
Technically, a dissent is obiter in its entirety.