Windows Registry is a hierarchically structured database that is used to store data related to configuration settings, software and user preferences in a Microsoft Windows Operating System (OS). It contains entries and values that control the behavior of certain configurations and user preferences, as well as information for OS components and applications that operate at a low level.
Most Windows applications write entries into the Windows registry during the installation process.
Source: https://www.techopedia.com/definition/5001/windows-registry