The portion of a packet, preceding the actual data, containing source and destination addresses and error-checking fields.
1. In word processing or printing, text that is to appear at the top of pages. A header might be specified for the first page, all pages after the first, even pages, or odd pages. It usually includes the page number and may also show the date, the title, or other information about a document. Also called: heading, running head. Compare footer.
2. An information structure that precedes and identifies the information that follows, such as a block of bytes in communications, a file on a disk, a set of records in a database, or an executable program.
3. One or more lines in a program that identify and describe for human readers the program, function, or procedure that follows.