Performance Improvement Plan, they are not unique to Amazon, most places have them though the process may differ. Not to be too cynical but ultimately they’re a way to document that you’re not meeting expectations - before being fired. Should there be any sort of employment claim later its a mechanism by which an employer can show documentation that any issues related to your being let go were performance related and not some sort of protected status or prejudice.
Outside of someone protected by a labor union, I’ve very rarely seen anyone recover from a PIP and not be eventually let go. Most commonly employees see them as a 30 or 60 day window to proactively find a new job before they’re terminated.
I think that's a bit simplistic. I've had coworkers that became better employees over time. The "problem" with PIPs is by the time you've screwed up long enough to be put on a PIP everyone knows there's no turning back.
For example, a friend I have that recently left Facebook knew for a good 6 months he needed to shape up. But they hadn't put him on a PIP in that time. They eventually offered him a decent severance to quit, and he took that rather than continuing to try. If he stayed, he probably would have been put on a PIP fairly shortly. It was the best thing for everyone. He wasn't all that happy there anyways.
Outside of someone protected by a labor union, I’ve very rarely seen anyone recover from a PIP and not be eventually let go. Most commonly employees see them as a 30 or 60 day window to proactively find a new job before they’re terminated.