Header

A masonry wall unit of brick which is laid so that its short end is exposed.

A pipe from which two or more tributary pipes run.

The first part of a received e-mail message which contains information about the routing of the message while traversing the Internet such as the Subject, origin and destination email addresses, the path an email takes, or its priority. Much of this may not be displayed if the e-mail software program keeps it hidden (usually an option).

The portion of a message that contains information used to guide the message to the correct destination. Note: Examples of items that may be in a header are the addresses of the sender and receiver, precedence level, routing instructions, and synchronizing bits.