Physical input means direct interaction with a device through a keyboard, mouse, touchscreen, console cable, or similar local control. It is the most basic way to operate a system, especially during first boot, recovery, or provisioning when remote management is not yet available. In practice, it is the moment when a person can type credentials, accept prompts, choose settings, or unlock a machine at the console.
In cyber security, physical input matters because local access can change trust boundaries. An attacker with hands-on access may be able to bypass weak screensavers, boot from external media, enter firmware settings, or approve actions that remote defenses would block. Defenders also rely on physical input for safe setup, maintenance, and incident response, but they should treat it as privileged access. Once a device is configured, limiting who can provide physical input is part of protecting the system.