Odd. I've been doing eng management at Google for the better part of a decade and I've never heard the term "Perf Room" before, nor did an internal search turn anything up. Maybe it is used, but at the very least I'm unaware of it.

I realize you worked there for a few months a few years ago, but I think someone might have been pulling your leg if they told you that phrase. (But you're right, like most meetings at Google, calibration meetings do happen in rooms. They're just normal conference rooms, though. Nothing special.)

For everyone else: calibration is a process where other managers at Google cross-check the performance scores given to employees across different teams and parts of the company. We do this so that an individual manager can't introduce undue bias or play favorites, and so an engineer at a given level in one part of the company is more or less the equal of an engineer at the same level in another part.

Calibration is one part of the system I think works really well, much better than any other place I've worked. In fact, I think more companies might want to emulate it.