On this tab you can view the properties inherited from the parent web part and override their default values. This allows you to create a specialized web part that can be created and used immediately without requiring any additional configuration.
To edit a property, clear the Inherited check box next to it and enter a new value into the given field. When new instances of the web part are created, their properties will be configured according to the specified values.
Any changes must be confirmed by clicking the OK button.
More resources can be found at Developer's Guide -> Development -> Web parts -> Overview.