noun

• (US) A board placed temporarily upon a dam, river, stream, etc. (typically within a permanent frame) to raise the water above its usual level.
• (by extension) A board that controls the flow of any material.
• (physics) A sheet of material that is subjected to an electric pulse or flashover in order to produce plasma.
• Any automated display that shows temporary information.
• An electronic display that shows the winning values in various gambling games such as keno or bingo.
• (education) An acrylic board used to display children's work in a school.
• (education) A board for displaying language material in the classroom, used like a flashcard but potentially holding more information.
• (historical) A device used in the 1920s for teaching typing skills which provided feedback on which key was pressed by lighting up the corresponding value.