A system bus is a communication pathway that connects different components of a computer, such as the CPU, memory, and input/output devices. It allows these components to exchange data and instructions, enabling the computer to function effectively. The system bus consists of three main parts: the data bus, address bus, and control bus. The data bus carries the actual data being transferred, while the address bus specifies the location of the data in memory. The control bus sends control signals to manage the operations of the system. Together, these buses facilitate smooth communication within the computer system.