Header

A header is a piece of information placed at the top of a document, page, or data record that identifies or describes its content. Headers are used to convey metadata, establish structure, and aid navigation across different contexts.

In publishing and word processing, a page header appears at the top of pages and may include the document title, author, chapter name, page numbers, or other running information. Headers are distinct from footers and are often repeated on each page.

In digital communications, headers carry metadata about a message or request. HTTP headers describe attributes of a request or response, such as content type and length, caching policies, and cookies. An email header lists sender and recipient addresses, dates, and routing details. In HTML5, a header element defines a site or section heading region and commonly contains a logo, title, and navigation.

In programming, a header file collects declarations and definitions shared by multiple source files. Header guards prevent multiple inclusion. Other domains use headers to tag files or streams with identification and version data.

In data organization, a header row labels columns in a table or spreadsheet, helping users understand the data and enabling software to map fields correctly.