head·er / ˈhedər/ • n. 1. Soccer a shot or pass made with the head.2. inf. a headlong fall or dive.3. a brick or stone laid at right angles to the face of a wall. Compare with stretcher (sense 4).4. a line or block of text appearing at the top of each page of a book or document. Compare with footer (sense 2).5. (also header tank) a raised tank of water maintaining pressure in a plumbing system.6. a beam crossing and supporting the ends of joists, studs, or rafters.

header Some coded information that precedes a more general collection of data and gives details about it.

The header of a data-structure representation is logically distinct from the data elements themselves and may serve several purposes:

(a) to hold global information about the whole structure, e.g. list length, array index bounds;

(b) to represent an empty structure;

(c) to provide links into the structure, e.g. pointers to first and last nodes in a list;

(d) to represent the entire structure in any other data structures of which it may be a part.

In networking, the header (or head) of a cell or packet is the part that holds routing and control information used to control the passage of the cell or packet across a network.

header. Brick or stone with its longer dimension buried within the wall and the smaller face exposed. See also brick.