Head"er, (-&etilde;r), n. 1. One who, or that which, heads nails, rivets, etc., esp. a machine for heading.

2. One who heads a movement, a party, or a mob; head; chief; leader. [R.]

3. (Arch.) (a) A brick or stone laid with its shorter face or head in the surface of the wall. (b) In framing, the piece of timber fitted between two trimmers, and supported by them, and carrying the ends of the tailpieces.

4. A reaper for wheat, that cuts off the heads only.

5. A fall or plunge headforemost, as while riding a bicycle, or in bathing; as, to take a header. [Colloq.]

• The upper portion of a page (or other) layout.
        If you reduce the header of this document, the body will fit onto a single page.
  
• Text, or other visual information, used to mark off a quantity of text, often titling or summarizing it.
        Your header is too long; "Local Cannibals" will suffice.
  
• Text, or other visual information, that goes at the top of a column of information in a table.
        That column should have the header "payment status".
  
• (informal) A font, text style, or typesetting used for any of the above.
        Parts of speech belong in a level-three header. Level-two headers are reserved for the name of the language.
  
• a brick that is laid sideways at the top of a wall or within the brickwork with the short side showing; compare stretcher
        This wall has four header courses.
  
• a machine that cuts the heads off of grain etc
        They fed the bale into the header.
  
• (football) the act of hitting the ball with the head
        His header for the goal followed a perfect corner kick.
  
• a headlong fall or jump
        The clown tripped over the other clown took a header.
  
• (computing) the first part of a file or record that describes its contents
        The header includes an index, an identifier, and a pointer to the next entry.
  
• (networking) the first part of a packet, often containing its address and descriptors
        The encapsulation layer adds an eight byte header and a two byte trailer to each packet.