Life Imprisonment

When a prisoner is sentenced to spend the rest of their life in prison. A very useless sentence, because once a prisoner gets it, they might as well have the death penalty. Either way they're going to die in prison. There are three types of life sentences.

Life With Parole:

When the prisoner gets sentenced to life, but is eligible for parole release after a certain number of years (usually 25 years). This is the most common sentence, as it ensures the prisoner will have an incentive to behave in prison, and it allows them back into society on strict monitoring. It's not a guarantee, to earn parole, you must behave very well in prison and show that you're worthy of being released.

Life Without Parole:

Life Imprisonment with no parole eligibility. If you get this, you're spending the rest of your days behind bars no matter what, unless you get the governor of your state to grant you clemency. This is hard to do, and the fact that you're likely a murderer isn't going to earn you much sympathy. But, if you truly can convince the governor you've changed, it might be worth a shot.

Practical Life Sentence

Any sentence that is longer than the prisoner will likely live. Generally, sentences higher than 75 years in prison fit this category, as even a young adult likely won't live to see their release date. These are handed out usually when a person has many crimes stacked against them, with no single one worthy of a life sentence, but adding up to like 100 years.

Two US states have Abolished Life Imprisonment.

Alaska, which still hands out the practical life sentence of 99 years in prison

Connecticut, which has lowered its maximum prison term from life to 25 years.

Also, some states have abolished life without parole, but still hand out life sentences with parole eligibility. These are:

Rhode Island
New York
Illinois
Washington