When Microsoft announced Windows 8 apps, there was a concept of tiled applications, rather than typical Windows menus, toolbars, and other controls. A tile becomes your content display area as well as your action item. Apps are swappable and paging is horizontal than vertical. These apps were called Metro Style apps. Since these apps were targeting Microsoft's newest operating system Windows 8, some people referred them as Windows 8 apps.

Later in Sept, I believe there was a copyright/trademark disputed and Microsoft was forced not use name term “metro style” anymore and the Metro Style apps were changed to Windows Store apps.

But what I am still seeing is, developers are still calling these apps, Windows 8 apps. I understand these app target Windows 8 operating system but it does not mean they won't work on Windows 9 or beyond. I see some authors are still using term Metro Style apps.

C# Corner has many articles and tutorials on Windows Store apps. Check out Windows Store apps here >>