Any schema or Table or Report which gives you meaningful information  of  one attribute  wrt more than one attribute is called  a cube.

For Ex: In a product table with Product ID and Sales colomns , we can analyse Sales  wrt to Prodcut Name , but if you analyse Sales wrt Product as well as Region( region being attribute in Location Table) the report or Resultant table or schema would be Cube.

ETL Cubes : Built in the staging area to load frequently accessed reports  to the target.

Reporting Cubes : Built after the actual load of all the tables to the target depending on the customer requirement for his business analysis.