Metadata or data about describes the details about the data in data warehouse or in data mart Such descriptions may be in term of contents and source of data that flows in Data warehouse or data mart. Components of metadata of data warehouse or data mart may include;
1-Description of sources of the data.
2-Description of Customization that may have taken place as the data passes from data warehouse into data mart.
3-Description information about data mart, it table, attributes and relationships etc
4 Definition of all types.

Source: Data Warehousing by C.S.R Prabhu

We will write more about metadata in coming posts! stay tuned.