header (Noun) — A line of text serving to indicate what the passage below it is about. ex. "the header seemed to have little to do with the text"
header (Noun) — Horizontal beam used as a finishing piece over a door or window.
header (Noun) — Brick that is laid sideways at the top of a wall.
header (Noun) — A framing member crossing and supporting the ends of joists, studs, or rafters so as to transfer their weight to parallel joists, studs, or rafters.
header (Noun) — A machine that cuts the heads off grain and moves them into a wagon.
header (Noun) — (soccer) the act of hitting the ball with your head.
header (Noun) — A headlong jump (or fall). ex. "he took a header into the shrubbery"