Metadata has multiple definitions, the briefest of which is "data about data." It can generally be thought of as information that describes, or supplements, the central data. For example, metadata produced by digital still cameras describe the settings used for the picture, such as exposure value or flash intensity. In such cases, the metadata can be considered as extra data, which merely add information, and is not critical to the functions of the main data. In other cases, such as on a Zip disk, metadata provides information regarding the write-protected status of the disk. In such a case, then, metadata can be considered essential to the proper functioning of the main product. Since the difference between data and metadata is often subtle and context-specific, rigorous definitions are elusive.
