Definition - What does Hard Reboot mean?
A hard reboot is the process of restarting a computer manually, physically or using any other method besides restarting it from the operating system controls. This allows a user to restart a computer, which is usually done when the operating system or software functions are not responding.
A hard reboot may also be called a hard restart, cold reboot or cold restart.
Techopedia explains Hard Reboot
A hard reboot is primarily done when a computer system freezes up and won’t respond to any keystroke or instructions from the user. Generally, a hard reboot is done manually by pressing the power button until it shuts down and pressing it again to reboot. Another unconventional method is by unplugging the computer from the power socket, plugging it back in again and pressing the power button on the computer to reboot it. This differs from a soft reboot, in which a user can press CTRL-ALT-DEL and restart the programs and OS without shutting down and restarting the whole system.
A hard reboot is not a recommended technique because restarting a computer without OS support can result in data loss, incomplete installations and suspension and corruption of any processes that were running before the reboot.