Metadata is often referred to as 'data about other data'.
(A) In a Digital Asset Management context it refers to descriptive information applied to assets to support a task or activity.
(B) With a file system, the data is contained in its files and directories, and the metadata tracks information about each of these objects: Is it a regular file, a directory, or a link? What is its size, creation date, last modified date, file owner, group owner, and access permissions?