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.

The situation where a promising idea / proposal / project either dies or is in development far too long and thus emerges too late, missing its moment, because of excessive amendment-and-approval requirements.

"Imprisoned in the elevator" is usually a product of:
(a) there being too many people in the organization whose sole purpose seems to be to wander around finding pies to put their fingers in but who add nothing to the "recipe" even though they can force others to make changes; or
(b) mandated internal processes which mandate that the approvals process be repeated for every change to the project, however minor; or
(c) managerial timidity, because moving something up and down is easier than risking one's neck with a firm yes or no.

Result: a viable or even great idea doesn't make it out the door on time or at all because it keeps repeatedly moving up and down the approval levels as each change has to be reviewed, re-reviewed and approved and re-approved The project stays in the building because it has been imprisoned in the elevator, never getting out, just forced to go up and down.