Metadata
Metadata (meta data, or sometimes metainformation) is "data about data", of any sort in any media. An item of metadata may describe an individual datum, or content item, or a collection of data including multiple content items and hierarchical levels, for example a database schema. In data processing, meta-data is definitional data that provides information about or documentation of other data managed within an application or environment.
For example, meta-data would document data about data elements or attributes, (name, size, data type, etc) and data about records or data structures (length, fields, columns, etc) and data about data (where it is located, how it is associated, ownership, etc.). Meta-data may include descriptive information about the context, quality and condition, or characteristics of the data.
Metadata in webpages
Metadata is typically included in the source of a webpage (HTML / XHTML) to help search engines drive relevant traffic to the site.
Below is some example metadata from this website:
<meta name="Description" content="kwiboo is a Software and ...." />
<meta name="Keywords" content="Software Development, E-Commerce, ...." />