What is header? - Definition from WhatIs.com
Part of the Computing fundamentals glossary:

In information technology, a header is, in general, something that goes in front of something else and is usually repeated as a standard part of the units of something else. A header can consist of multiple field s, each containing its own value. Here are four common uses:

1) In a document , a header is some combination of text and image s that can be made to appear at the top of each page when displayed or printed.

2) In e-mail , the header is the part of a message that describes the originator, the addressee and other recipients, message priority level, and so forth.

3) In a computer file, a header may be a field that precedes the main file content and describes the length of the content or other characteristics of the file.

4) In a network transmission unit, a header precedes the data or control signals and describes something about the file or transmission unit, such as its length and whether there are other files or transmission units logically or physically associated with this one.

This was last updated in May 2005
Posted by: Margaret Rouse

Related Terms


  • irrational number

    - An irrational number is a real number that cannot be reduced to any ratio between an integer p and a natural number q. (WhatIs.com)

  • Cartesian coordinates (rectangular coordinates)

    - Cartesian coordinates, also called rectangular coordinates, provide a method of rendering graphs and indicating the positions of points on a two-dimensional (2D) surface or in three-dimensional (3D... (WhatIs.com)

  • algorithm

    - An algorithm (pronounced AL-go-rith-um) is a procedure or formula for solving a problem. Algorithms are used throughout almost all areas of information technology. (WhatIs.com)


  • Computing fundamentals

    - Terms related to computer fundamentals, including computer hardware definitions and words and phrases about software, operating systems, peripherals and troubleshooting.

  • Internet applications

    - This WhatIs.com glossary contains terms related to Internet applications, including definitions about Software as a Service (SaaS) delivery models and words and phrases about web sites, e-commerce ...

Tech TalkComment



    Contribute to the conversation

    All fields are required. Comments will appear at the bottom of the article.