A life sentence is an imprisonment with no time limitation (i.e. – with no possibility of release for the prisoner) as long as it has not been limited.
 
The authority that may limit (in years) a life sentence for a prisoner is the president.

There are offences, such as murder, that the judge who had convicted a man of committing them must sentence the guilty person to a life sentence.
 
In other case in which there is no legal obligation to sentence a life sentence, the judge uses his authority to sentence the prisoner to a life sentence – this imprisonment shall be a period of 20 years.