A header may refer to any of the following:
1. A header is text at the top of a page in an electronic document or hard copy. For example, in Microsoft Word, a header could be created in a document to display the page number in the top corner of each page. By contrast, a footer is at the bottom of a page in an electronic document or hard copy.
2. On a web page, the header is the top portion of a web page that contains the company name and logos. Contained between opening and closing <header> tags, this section also often contains a navigation bar to help users move between common areas on the site.
A header should not be confused with an HTML head or heading or the header that describes the page as mentioned below.
3. A web page header may also refer to data sent to a browser from a web server. The web page header data is not displayed to the user, but provides important information to the browser about how to display the content.
4. When talking about the motherboard, a header can refer to pins on the motherboard that allow additional ports to be added to the computer. See our 1394 and USB header definition for further information.
5. More commonly known as an e-mail header, a header is data contained at the beginning of an electronic message that contains information about its contents. The header is used to identify the message, its source and destination, as well as other information that may be required to decode and understand it. The technical specifications on e-mail headers is also available in RFC821, RFC822, and RFC2045.