Matrix management is a workplace organization system that is popular among tech workplaces. You can read it about it here:

https://en.wikipedia.org/wiki/Matrix_management

I will explain matrix management in simple terms: Instead of having a single boss, you have two (or possibly more) bosses: A teacher-boss and a work-boss. The purpose of the work-boss is to let you know what work needs to be done. Since you go to work in order to do work, the work-boss is the one you are in most frequent contact with. The teacher-boss has only one role in your career, which is that at the end of the year he writes your performance evaluation. So even though you may go months and months without ever talking to your teacher-boss, the teacher-boss is in reality much more important than your work-boss.

What's the effect of a system like this? What happens when the person who writes your evaluation is completely disconnected from and indifferent to the work you do? What happens is that merit does not matter and instead politics dominates. In the traditional system, if you are a good worker but upper management wants to give you a low rating, your boss may argue against upper management to give you a higher rating, because he knows he will be screwed if he loses you. But this is not the case in the matrix system.