noun
A very large outdoor sign, generally used for advertising.
(dated) A flat surface, such as a panel or fence, on which bills are posted; a bulletin board.
(nautical) A piece of thick plank, armed with iron plates, and fixed on the bow or fore-channels of a vessel, for the bill or fluke of the anchor to rest on.
(television, radio) An opening or closing portion of a program, often including credits and sponsors' names.
(computer graphics) A sprite that always faces the screen, no matter which direction it is viewed from.
verb
(transitive) To advertise on a billboard.