Derogation

Derogation (Latin "derogatio") is the relaxation or exemption from of a rule of law. This is as opposed to a repeal or ending of a law. The term is used in both civil law and common law. It is sometimes used, loosely, to mean abrogation. For example in the legal maxim: "Lex posterior derogat priori" which means a more recent law may overrule an earlier law. Derogation is different from dispensation (an to a law) in that it applies to the law. A dispensation applies to specific people who are affected by the law.
In terms of European Union legislation, a derogation can also imply that a member state delays putting into effect a part of an European Union regulation (etc.) into their own legal system. This can be for a period of time such as five years. Or that a member state has decided not to enforce a specific provision in a treaty due to internal circumstances (typically a state of emergency).