Information about data, including the format of the data element, which application system owns it, where it is located, and how it should be used. Metadata is the global information about what data exists across the enterprise and the standards applying to that data. It is very important to the data warehouse effort because it sets the standards and the rules used for data transformation and cleansing.
Data about data. The definition and scope of metadata depends upon context. In the context of Information Management, metadata is generally thought of as providing information (what database stores it? what data type is it? how long is the field? etc.) about a data element. Within the context of Data Governance, the term also includes “business” metadata such as the names and roles of Data Stewards. Metadata repositories are employed to store and report on metadata.
SOURCE: Data Governance Institute