Integral service in Windows since Windows Vista that updates Windows components, including installed components and drivers, and certain other Microsoft software, notably Office.
Microsoft Windows Update is an integral service in every modern Windows operating system, that gives users the ability to update the Microsoft software and operating system in their computers, including installed components and drivers.
Starting with Windows Vista, all Microsoft product updates are no longer performed through the Microsoft Update Website. Included with the operating system, the Automatic Updates control panel has been expanded to access the new and revised Microsoft's Windows Update service.
Users of modern Windows operating systems by default no longer perform manual updates to their Microsoft products (including the operating system). The operating system performs automatic searching and installation of updates. Prior to Windows 10, users could configure Windows Update to not perform automatic updates, or to inform them before installing new updates.
Windows Update (Microsoft Help Website).
Windows Update (at Wikipedia).