Input/Output

In computing, input/output (I/O, i/o, or informally io or IO) is the communication between an information processing system, such as a computer, and the outside world, such as another computer system, peripherals, or a human operator. Inputs are the signals or data received by the system and outputs are the signals or data sent from it. The term can also be used as part of an action; to “perform I/O” is to perform an input or output operation.

I/O devices are the pieces of hardware used by a human (or other system) to communicate with a computer. For instance, a keyboard or computer mouse is an input device for a computer, while monitors and printers are output devices. Devices for communication between computers, such as modems and network cards, typically perform both input and output operations. Any interaction with the system by an interactor is an input and the reaction the system responds is called the output.
— Input/output - Wikipedia

(I/O) communication between a computer and its users, its storage devices, other computers (via a network) or the outside world.

Some examples of I/O operations:

• HTTP requests (sending/receiving data over network)
• access to database
• reading/writing files
• Printing to screen

Important aspects of I/O are throughput, latency, and whether the communications are synchronous or asynchronous (using some kind of buffer).