SpidersWeb :
The TDP value is provided by Intel, so that OEM part makers can ensure their system will deal with xxxW of heat - this allows them to use the fastest processor in that range/stepping without overheating. Intel's stock heatsinks are designed with this number in mind.
Absolutely.
During testing, Intel does measure the highest temp a CPU could conceivably get to; there's a test sequence known colloquially as the "power virus" (because it keeps generating more power, which slows the chip down, hence generating more power to run the test... etc.). We used to quote this as max power or something equally sensical, but there were two problems with this:
1) the power virus was never in any way indicative of real world conditions. (And believe me, any attempt by anyone internal to suggest that "it's something that the customer will rarely, if ever see" was shot down faster than you can say "Pentium debacle"). It was a theoretical maximum, but it was actually impossible to duplicate in a real system for various reasons.
2) since no application ever came remotely near this power (and everyone knew it), some motherboard and heatsink/fan makers tried to save cash by designing around what their best guess of the power dissipation would really be. Sometimes they guessed wrong, and since Intel's name was on the CPU we caught the blame (most consumers don't even know what a motherboard is). Something needed to be done to make the design power numbers rational, and TDP was the result.
There's actually considerable effort put forward in each processor generation to characterize (and re-characterize) what the appropriate mix of conditions is in order to closely measure the TDP. It's in Intel's interest to make the TDP as accurate as possible because without it the part's going to throttle a lot and look like crap in the field (and, of course, in benchmarks).
It's a
marketable term, but it's not a
marketing term. If it were subject to significant tinkering from folks who just want to make a sale, you'd see a bunch of "35W TDP" parts and motherboards and coolers drastically undersized for the power delivery and dissipation required.