Default Measures and Members allow you to define which Members are used to slice the data by default, when the Dimension or Measure is not explicitly used in a query.

 

For example, if your data contains sales information and you wish the dashboards you create always to be in the context of a specific product, you would set that specific product as the default Member by right-clicking it and navigating to ‘Set as Default’.  The currently set default Member is highlighted in bold.

 

Similarly, setting of the default Measure is done by right-clicking the Measure and navigating to ‘Set as Default’.