Definition of headers:
(n) :
The upper portion of a page (or other) layout.
(n) :
Text, or other visual information, used to mark off a quantity of text, often titling or summarizing it.
(n) :
Text, or other visual information, that goes at the top of a column of information in a table.
(n) :
(informal) A font, text style, or typesetting used for any of the above.
(n) :
(computing) The first part of a file or record that describes its contents.
(n) :
(networking) the first part of a packet or stream, often containing its address and descriptors.