(
Universal 
Windows 
Platform)  Introduced with Windows 10, UWP is a common programming platform for all Microsoft products, including Windows, Xbox, Surface Hub and HoloLens.  Applications written as UWP programs perform across all Windows devices, but rather than target an OS version, developers specify a device family.
UWP provides access to the WinRT programming interface (API) and Fluent user interface.  Apps are downloaded from Microsoft's app store (see 
Microsoft Store).  See 
Microsoft Fluent Design System and 
WinRT.