I/O (Input/Output) refers to the mechanisms by which a computer system exchanges data with external devices or subsystems. Input includes data received from sources such as keyboards, disks, sensors, and networks, while output includes data sent to displays, printers, storage devices, or network interfaces. Efficient I/O handling is critical to system performance, as slow or blocking I/O operations can significantly reduce responsiveness. Example: Reading a file from disk and displaying it on a screen both involve I/O.
