Derogation is the partial revocation of a law, as opposed to abrogation or the total abolition of a law. The term is used in both civil law and canon law. It is sometimes used, loosely, to mean abrogation, as in the legal maxim: Lex posterior derogat priori, i.e. a subsequent law imports the abolition of a previous one.
Derogation differs from dispensation in that it applies to the law, where dispensations applies to specific people affected by the law.
In terms of European Union legislation, a derogation can also imply that a member state delays the implementation of an element of an EU Regulation (etc) into their legal system over a given timescale, such as five years; or that a member state has opted not to enforce a specific provision in a treaty due to internal circumstances (typically a state of emergency).