Metadata is structured information that describes, explains, locates, or otherwise makes it easier to retrieve, use, or manage an information resource. Metadata is often called data about data or information about information. According to Tim Berners-Lee's axiom "metadata is data".
The term metadata is used differently in different communities. Some use it to refer to machine understandable information, while others use it only for records that describe electronic resources. In the library environment, metadata is commonly used for any formal scheme of resource description, applying to any type of object, digital or non-digital. There are three main types of metadata: descriptive metadata, structural metadata and administrative metadata, each of them contributing to the management of information resources and help to ensure their intellectual integrity both now and in the future (See: NISO, Understanding Metadata 2004).