The Windows Registry Editor is a built-in tool in the Windows operating system that allows users to view and modify the system's registry. The registry is a database that stores configuration settings and options for the operating system and installed applications. It plays a crucial role in how Windows operates, as it contains information about hardware, software, and user preferences. Users can access the Registry Editor by typing "regedit" in the Run dialog or the Start menu. However, caution is advised when making changes, as incorrect modifications can lead to system instability or malfunction. Always back up the registry before making any changes.