Metadata is data that describes other data. Digital files often include metadata to provide information about the file and its contents. For example, a digital image may include metadata like the date and time of the photograph, its location, and the camera and settings used. A text document's metadata may include metadata listing the author's name, the document's title, and a summary of its contents. Metadata does not usually appear when viewing a file, although it can often be displayed when needed.
Some metadata can be modified while editing a file, like specifying an author's name; other metadata is automatically set by the computer's operating system or the software creating the file, like a file creation date. Most modern file systems use an index of file metadata for file searches. This index allows you to quickly search your computer for files using the information in file metadata.
HTML files and websites frequently use metadata to provide information about the content of a webpage to search engines. HTML files contain meta tags that include information about the page — its author, a description, some keywords, or even special instructions that tell a web browser how to display the page contents. Search engines can use these tags when organizing and displaying search results.