Metadata is "data that provides information about other data", but not the content of the data itself, such as the text of a message or the image itself. There are many distinct types of metadata, including:

Descriptive metadata

The descriptive information about a resource. It is used for discovery and identification. It includes elements such as title, abstract, author, and keywords.

Structural metadata

Metadata about containers of data and indicates how compound objects are put together, for example, how pages are ordered to form chapters. It describes the types, versions, relationships, and other characteristics of digital materials.

Administrative metadata

The information to help manage a resource, like resource type, permissions, and when and how it was created.

Reference metadata

The information about the contents and quality of statistical data.

Statistical metadata

Also called process data, may describe processes that collect, process, or produce statistical data.

Legal metadata

Provides information about the creator, copyright holder, and public licensing, if provided.