Life imprisonment

Life imprisonment is a term used for a sentence of imprisonment. The effect of such a sentence is different in each jurisdiction. Life in prison is known by others as a humane alternative to the death penalty for the most serious crimes such as murder, terrorism, etc. A formerly used form of life imprisonment was Immurement.
In some cases, a person with a life sentence can leave prison on parole after a number of years. In the United States, this is usually 15 to 25 years. However, the person must convince a court or parole board that they will not commit more crimes. If a person leaves on parole, they are not completely free, and they have some restrictions. 
In other cases, the court may decide that the person should never leave prison, which is called life without parole. This sentence is used for even more serious crimes.