Most of the men I know in prison (I mostly know men) are serving some kind of life sentence. Some -- like Spoon -- are serving life without possibility of parole. Some -- like Coties -- have a sentence so long (99 years) that it stands as a life sentence. Others -- like Elmo -- are serving term-to-life (in his case, 7-to-life, a sentence meant to last about 13 years in the era when he was convicted, but he's now served over 30 years on that sentence).
Those with term-to-life sentences have to go before the Board of Prison Terms periodically and make a case for why they should be given a release date. There's lots to share about this process, but for now here's a very interesting article about one man -- Lonnie Morris, whom Spoon, Coties, Elmo, and I all knew at San Quentin 25 years ago -- and his experience with the Board.