It's referring to a section of the soft PPT (registry-based PowerPlay Table that many of us are using) that controls the SoC clock. By adjusting the values as mentioned, you can increase the SoC to 1200MHz from the Blockchain driver's hard default of 1107 MHz (which is why you cannot push memory clocks beyond this value), and thus increase those memory clocks beyond 1100-1105.

Consolidated context on this /r/MoneroMining thread