User wants to know how to turn Output Window off completely.
When the Automatically Show Output Window option is selected, the Output Window will automatically appear when errors, server output, or informational text are sent to it.
To deactivate this functionality/behaviour take these steps:
1. View > Preferences
2. Expand the General group and the User Interface subgroup.
3. Look down the list for Automatically Show Output Window and uncheck options (Errors, Server Output, Informstion) as appropriate.