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Microsoft Store

Microsoft Store (previously: Windows Store) is a curated digital distribution platform for apps, console games and digital video.
Competitors offer similar functionality through Google Play or Mac App Store.

Sideloading

The term sideloading refers to installing apps that haven't gone through the certification process (and thus don't show up in the Store).
By default, Windows does not allow to sideload apps.

See also

Are UWP apps always installed from Microsoft Store.
InstallService seems to be the service for Microsoft Store.
Apps from the Store seem to be installed under %PROGRAMFILES%\WindowsApps.
Apps for Windows 10 S can only be installed from Microsoft Store.
The SDK feature Windows App Certification Kit.

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