Input

Input is information, signals, or resources provided to a system to influence its operation or to be transformed into output. The term is widely used across disciplines—from computing and engineering to biology and economics—and generally contrasts with output, the result produced by a process. Depending on the context, input may be data, energy, material resources, or sensory information.

In computing and information technology, input describes data received by hardware or software from users or external devices. Common input sources include keyboards, mice, touchscreens, microphones, cameras, and various sensors. Input devices convert physical signals into digital data that a computer can process. Inputs can be real-time, such as a user typing, or batch, such as a file loaded into a program.

In programming, input refers to data supplied to a program during execution. It may come from user prompts, files, command-line arguments, network services, or standard input streams. Programs typically validate and parse input to ensure it meets expected formats, convert it to appropriate data types, and handle errors or unexpected values.

Other fields use the term with domain-specific meaning. In control theory and engineering, an input is a signal or stimulus that drives a system’s state. In biology and neuroscience, sensory input refers to information received through the senses. In information theory, input is the source data that enters a system for processing, encoding, or transmission.