Life imprisonment is a sentence of imprisonment for a serious crime, nominally for the entire remaining life of the prisoner, but in fact for a period which varies between jurisdictions: many countries have a maximum possible period of time (usually 50 years) a prisoner may be incarcerated, or require the possibility of parole after a set amount of time.
In jurisdictions without capital punishment, life imprisonment (especially without the possibility of parole) constitutes the most severe form of criminal punishment.