Intel® Turbo Boost Technology

Intel® Turbo Boost Technology Performance on demand
Intel® Turbo Boost Technology is one of the many exciting new features that Intel has built into latest-generation Intel® microarchitecture (codenamed Nehalem).
It automatically allows processor cores to run faster than the base operating frequency if it's operating below power, current, and temperature specification limits.Dynamically increasing performance

As an independent and complimentary feature, Intel® Hyper-Threading Technology (Intel® HT Technology) along with Intel Turbo Boost Technology increases performance of both multi-threaded and single threaded workloads. Intel Turbo Boost Technology is activated when the Operating System (OS) requests the highest processor performance state (P0).
The maximum frequency of Intel® Turbo Boost Technology is dependent on the number of active cores. The amount of time the processor spends in the Intel Turbo Boost Technology state depends on the workload and operating environment, providing the performance you need, when and where you need it.
Any of the following can set the upper limit of Intel Turbo Boost Technology on a given workload:
Number of active cores
Estimated current consumption
Estimated power consumption
Processor temperature
When the processor is operating below these limits and the user's workload demands additional performance, the processor frequency will dynamically increase by 133 MHz on short and regular intervals until the upper limit is met or the maximum possible upside for the number of active cores is reached. Conversely, when any of the limits are reached or exceeded, the processor frequency will automatically decrease by 133 MHz until the processor is again operating within its limits.