It is a condition where there is rise of body temperature after death instead of cooling of body. Although the process of postmortem glycogenolysis, which occurs in all bodies soon after death, can produce up to 140 calories which can rise the body temperature by about 2 degrees, yet the temperature shows further rise in all such conditions, e.g. asphyxial death, poisoning due to alcohol, dhatura and strychnine, brain-stem hemorrhage, deaths due to infectious diseases, etc.
References
Postmortem Caloricity Wikipedia(Text) CC BY-SA