Message dialog in Windows Store app
What is a message dialog in Windows Store app.
Message dialogs
Message dialogs are dialogs that require explicit user interaction. They dim the app window and demand a user response before continuing. Use message dialogs only when you intend to stop the user and to demand response.

In the example above, the app window is dimmed, and the user must tap one of the two buttons to dismiss the dialog. That is, the message in the dialog cannot be ignored.