For AM3+ boards that support the FX line of AMD CPU's, HPC mode is an option that tones down (or removes entirely) CPU throttling based on (IIRC) a current limit instead of a thermal limit.
Aside from removing throttling, it will also make the single-core Turbo the all-cores Turbo freq, effectively making it the "normal" full-speed even when all cores are loaded. I've tested it repeatedly in my now-dead FX-8350, and HPC mode consistently and predictably resulted in that behavior.
It's surprising that it's not well-documented, I only found out the info I gave above through testing and experimentation. There is no word on HPC mode either from the vendors or from AMD; at least, not that I could find myself.