CPU stands for central processing unit. It is a general-purpose processor that executes program instructions and coordinates much of a computer's work. Core count and clock speed describe parts of its design, but neither number alone predicts how fast every application will run.
Simple explanation
A CPU reads and executes instructions for the operating system and applications. It handles control-heavy and general-purpose work such as launching programs, processing input and coordinating data movement.
Modern computers may contain several CPU cores so independent work can progress in parallel when the software supports it.
Technical context
CPU performance depends on architecture, instructions completed per clock, frequency, core and thread resources, cache, memory, power limits, cooling and software. Comparing one specification across unrelated processor families can be misleading.
A CPU and GPU are complementary. CPUs are suited to varied, latency-sensitive instruction flows; GPUs provide many parallel execution resources for suitable workloads.
Practical example
A high-core-count processor can help a well-parallelized render, while a lightly threaded office task may depend more on per-core responsiveness. Start with the actual workload and supported software instead of buying by core count alone.
Sources and further reading
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