"I wanted to know what is meant by 'acceleration use only'."

That is neither an Intel nor Dell term so I have no idea in regards to CPU.

Perhaps you are referencing the marketing term TURBO Boost which is almost meaningless since

only the K models are unlocked.

Turbo boost is marketing not standard performance. " turbo boost " is just listed in specs to fool people and that you might get a boost it rarely if EVER happens. Maximum turbo frequency indicates the highest possible frequency achievable when conditions allow the processor to enter turbo mode.

Due to varying power characteristics, some parts with Intel® Turbo Boost Technology will not achieve maximum turbo frequencies when running heavy workloads and using multiple cores concurrently. Processors with the same model number running under the same operating conditions may see some frequency or power variance. This is a natural characteristic of silicon driven by variances in voltages, power, and leakage during the production process.