Included in the head section of an html web page and is visible to search engines but not human visitors. Meta tags provide information about a web page, like the topic (title), keywords, description and also instructions to search engine robots and visitor browsers.

Data about data. Meta data describes how and when and by whom a particular set of data was collected, and how the data is formatted. Meta data is essential for understanding information stored in data [..]

Meta data is information in the code that is not visible to the user, such as meta tags.

Meta data is the descriptive data that is contained in Meta tags.

 Business-critical data such as advertiser name, effective cost per thousand impressions (eCPM) goal, format, and version information.  

Data used to describe other data. Meta data is essentialy data about data.