The Windows Registry is a centralized hierarchical database that is used by Windows to store system settings, hardware configurations, and user preferences. The Registry can be explored by using a program called the Windows Registry Editor. When making a change to the Registry, it is recommended that you first create a export of the entries that you are about to modify. This allows you to save the information to a Registry file, or a test.reg file, so that if a problem occurs you can import the original settings back into the Registry.
Source: https://www.bleepingcomputer.com/tutorials/how-to-export-registry-key-in-windows/