CPU stands for central processing unit, the part of a computer's hardware that performs the instructions of programs and controls the operations of the system. Simply put, it is the brain of the computer.
The CPU is the most important part of a computer system and is where the arithmetical and logical calculations are made. If a computer has more than one CPU, it is a multiprocessor. Most modern CPUs are microprocessors, meaning they are contained on a single chip. When purchasing a computer, consumers should consider the CPU performance, or speed; the better the CPU, the faster the computer is.