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.