The Central Processing Unit (CPU) is the main component of a computer system, responsible for executing instructions and performing calculations. It is often referred to as the 'BRAIN' of the computer, as it is responsible for controlling all of the other components. The CPU is composed of several components, including the arithmetic logic unit (ALU), control unit (CU), and registers. The ALU performs mathematical operations, the CU controls the flow of data, and the registers store data temporarily. The CPU is connected to other components, such as memory, storage, and input/output devices, through a bus.