Metadata is often interpreted as “data about data” in the same way metathought is interpreted as “thought about thought.”

Metadata is data used for organizational purposes. Often, metadata is used to organize other types of data or data containers (the distinction between data and data containers is often inconsequential).

A public library is a classic example of metadata in action. In a public library, data is stored in books (which act as data containers, but are physically difficult to distinguish from the data they contain). Librarians use metadata to organize these books and the data they contain. Metadata describing books includes the book’s title, author, date of publication, and subject. A card catalog is a repository for metadata about library books.

Data is stored in a variety of formats besides books; data may be stored as maps, sheet music, images, and various other formats, and the metadata for each format will be different.

For example, metadata about a digital photograph usually includes the name of the photographer, resolution and color depth of the image, the type of camera that recorded the image, the date on which the picture was taken, the location at which the picture was taken, and the exposure of the image. Likewise, metadata about a map usually includes the map’s scale, projection, and date of publication.

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