billboard

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.

(computer graphics) A sprite that always faces the screen, no matter which direction it is looked at from.