a small piece of material, usually composed of wood or of cardboard, used to prevent a drink and its container from contacting a surface, such as a table, and leaving a mark. To protect the surface or a table or of a bar from drips or from condensation, drinkers or waiters position a coaster before parking a glass on top of that coaster.
a recordable compact disc which has not been recorded properly, and thus is useless as a data storage medium; by implication its only use is as a drink coaster.
