When someone returns an cruel favor to another after what has been done to them or an loved one.
Revenge has many different names and forms in many different cultures.
During the middle ages an insult was not thought to be over until revenge was carried out or at the very least paid for with a system known as wergild which translates into man-price an extensive Anglo-Saxon system which placed a varied monetary value on certain acts of violence in an attempt to limit the possible disastrous circle of revenge by specification of the punishment of such acts.
In Japan the Samurai class upheld the honor of their family, clan or lord through Katakiuchi the practice of revenge killings which involved not only the offender but also the relatives of the offender. Today though Karakiuchi is still an important part of Japanese culture but is mostly pursued peacefully.