It is a tool that indicates the relative likelihood that it has what you're looking for. The weird thing, unless you look at it compared to the other relevancy numbers, it doesn't make much sense.
I understand the purpose of the tool in theory. I am asking, however, why these particluar scores are being displayed for us to see on this particular bulletin board. If there is some helpful purpose for them, I would like to understand it. On the other hand, if as stated upthread, these scores don't mean much in an absolute sense, I'm still curious why they are being displayed.