So, the scale is from 1 to 7.
1= you shouldn't even be here anymore (not meeting expectations)
2= expect a PIP and to be terminated (needs improvement)
3= expect to be laid off when times are lean or strategic realignments happen (consistently meets)
4= the realistic minimum each employee needs to meet to be left alone (consistently meets+)
5= you actually are contributing a decent amount, whether that is brute force hours (60+) or working smart (learn how to reuse stuff and minimize email/meetings without hurting work quality)
6= you're doing work at the next level and could be up for promotion in a a few cycles
7= you're definitely doing work at the next level and could be up for promotion in a few cycles
Everything is keyed to your performance review rating and market ratio. The rating is as mentioned above; the market ratio is how QC pays for your job versus how the industry pays for the job.
Low rating, low market ratio = don't expect much, at least you don't cost much
High rating, low market ratio = good merit increase, you're doing well
Low rating, high market ratio = no raise likely, you're not worth it
High rating, high market ratio = you've pegged the meter; you need a promotion, especially if you get a one-time lump sum with no merit increase at review time.
There are separate bonus and stock ratings to go with the merit increase rating; they should be related but not necessarily equal. Bonus is for the work you did this past cycle, stock is the carrot for keeping you in the future. If you get a low merit rating (3 and below), don't necessarily expect any bonus or stock. If you get a 4 or higher then you should see something.
None of this should be a surprise. Basically all companies have HR departments that follow the same table-based approach to merit/bonus/stock, all keyed from ratings. The ratings are argued in group sessions among managers, adjusted, and then people higher up in the management chain start fitting the population based on the aggregate pools.
Most individual contributors don't realize how the process works. It's no mystery. Do your job, do a little more than your job, have a good personality and be a team player helping others around you, learn some stuff, do process improvements, publish/contribute stuff, and actively manage your career/outcome, and you'll be ok. But if you expect to get high marks when you have to be told what to do, and you require lots of supervision, and you quit after 40 hours, and you don't try to learn anything, and you don't work for the benefit of the company, well you're a 3 maybe.