Grain definition in the context of OBIEE.
The following list describes the different grains in navigating a query:
Select quarter, myMetrics from MySubjectArea
In 11g, the hierarchical column determines the grain of the report.
When the query grain match the aggregation grain of a logical table source, this one is used to create the physical query.
You can also define a aggregation grain calculation on a measure. This kind of calculation creates level-based measure.