Typically used to make repairs to or save data from the Windows registry. Use, with caution, the Windows Registry Editor to create a .REG file. All you have to do is "run" the file (double click on it) in order to insert the values into the registry.
Do this with even more caution! Changing the registry improperly can result in your system no longer working.
Note: This file type can become infected and should be carefully scanned if someone sends you a file with this extension.