"Sanctions" is the plural of sanction (see also penalty). Below the specific use of the plural is discussed.
Penalties, usually monetary fines, levied against a party to a legal action or his attorney, for violating rules of procedure, or for abusing the judicial process. The most severe sanction is the involuntary dismissal, with prejudice, of the complaining party's cause of action, or of the responding party's answer. This has the effect of deciding the entire action against the sanctioned party without recourse, except to the degree that an appeal or trial de novo may be allowed because of reversible error.
Almost always used in the plural, even when it refers to a single event. If a judge fines a party, it is not said that he imposed a sanction, but that he imposed sanctions.
Sanctions can also be coercive measures adopted by a group of nations in an effort to influence another nation into following international law or submitting to judgment.