A miscarriage of justice primarily is the conviction and punishment of a person for a crime they did not commit. The term can also apply to errors in the other direction—"errors of impunity", and to civil cases. Most criminal justice systems have some means to overturn, or "quash", a wrongful conviction, but this is often difficult to achieve. The most serious instances occur when a wrongful conviction is not overturned for several years, or until after the innocent person has been executed or died in jail.
"Miscarriage of justice" is sometimes synonymous with wrongful conviction, referring to a conviction reached in an unfair or disputed trial. Wrongful convictions are frequently cited by death penalty opponents as cause to eliminate death penalties to avoid executing innocent persons. In recent years, DNA evidence has been used to clear many people falsely convicted.
While a miscarriage of justice is a Type I error for falsely identifying culpability, an error of impunity would be a Type II error of failing to find a culpable man guilty.
Scandinavian languages have a word, the Swedish variant of which is justitiemord, which literally translates as "justice murder." The term exists in several languages and was originally used for cases where the accused was convicted, executed, and later cleared after death. With capital punishment decreasing, the expression has acquired an extended meaning, namely any conviction for a crime not committed by the convicted. The retention of the term "murder" represents both universal abhorrence against wrongful convictions and awareness of how destructive wrongful convictions are. Some Slavic languages have also the word (justičná vražda in Slovak, justiční vražda in Czech) which literally translates as "justice murder", but it is used for Judicial murder.
Also, the term travesty of justice is sometimes used for a gross, deliberate miscarriage of justice. The usage of the term in a specific case is, however, inherently biased due to different opinions about the case. Show trials (not in the sense of high publicity, but in the sense of lack of regard to the actual legal procedure and fairness), due to their character, often lead to such travesties.
The concept of miscarriage of justice has important implications for standard of review, in that an appellate court will often only exercise its discretion to correct plain error when a miscarriage of justice (or "manifest injustice") would otherwise occur.