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:
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.