What is the terms for life imprisonment?

It is imprisonment till death.

commonly known term of 14 yrs is only for counting purposes  in cases where sentence has been commuted under Art 161 or Art. 72 of the constitution. s 55 of IPC provides that the appropriate Govt may commute life sentence into one not exeeding 14 yrs. s. 433-A of CrPC provides that a life sentence can not be commuted to a sentence for less than 14 yrs if offence for which sentence was awarded ws one for which death sentence is also provided.

There are decisions of supreme court also to the effect that life imprisonment means imprisonment  till death. Thus general notion about 14 yrs period is a misconception on basis of  remission and commutation of sentences.