That's what it is, I am pretty sure.
There is a simpler definition but it is too colloquial)
Blue Board IS a fantastic tool and helps translators a lot. Agencies (and I know it not from someone, but from my personal talks with several Project Managers in the reputable translation agencies) really pay attention to the translators' comments and their (agencies') Blue Board rating.
I was told by a colleague in the US the other day that someone posted his opinion about an agency on PROZ Blueboard and had to himself face legal action, despite the fact that the agency had not paid him anything for the work he did. It seems the agency aleeged that the translator ruined their iamge.
Does posting your honest opinions on the blueboard make a translator vulnerable ?? May be a topic of interest to all of us?