A registry tweak refers to the manual modification of settings within the Windows Registry, a database that stores configuration options for the operating system and installed applications. By using the Windows Registry Editor (regedit), users or administrators can change how Windows behaves, enable or disable features, and optimize performance or security. Registry tweaks are often used to customize the user experience or to apply configurations not available through standard system settings. However, improper changes to the registry can cause system instability or security vulnerabilities, so such tweaks should be performed with caution and ideally backed up beforehand.