Doctor of Philosophy? -- that's the canonical meaning. Permanent Head Damage? -- that's a good one. But the one I came across many months ago and believe that it is very interesting is this quotation from Rondam Ramblings' "Top ten geek business myths".

The only thing a Ph.D. means is that you're not a moron, and you're willing to put up with the bullshit it takes to slog your way through a Ph.D. program somewhere.

Please check out the full article.

I don't have a Ph.D. yet but I believe that I am not a moron, though. Hence, getting a Ph.D. will benefit me only the second phrase :D.