At Google you do a "self-assessment" for your annual review, and you pick some number of peer reviewers who you want to also provide feedback. Your manager can add or subtract from this list. Your manager then provides that perspective and a rating that is normalized across the organization through managerial "calibration meetings".

This turns into your annual (sometimes 6 monthly) review packet.

In engineering, you and/or your manager can decide to put you up for promotion.

In this case, your review turns into a "promo packet", and it is sent to a promotion committee who decides whether you are clearly operating at the next level.

A critical point is that your peer reviewers can see a 'P' next to your feedback request, so they know if you are up for promotion. In theory, promo feedback should match normal review feedback, but in practice promo feedback follows game theory dynamics.

It's a precis of what an IC has achieved over the last performance cycle. Can't speak for Google, but where I am it's focussed on the impact you've achieved in various axes.

A promo packet is a document explaining why you should be promoted. Includes link to the evidence, your design docs, your check-ins, and anything else you think might help.