在立体几何中，立体几何体的邊界被称作面或表面，更嚴謹地說，面是立体几何体的一個平坦表面，而不平坦的面通常稱為曲面，而所有表面的總和稱為表面積。
The basic building block of a battery. It is an electrochemical device consisting of an anode and a cathode in a common electrolyte kept apart with a separator. This assembly may be used in its own container as a single cell battery or be combined and interconnected with other cells in a container to form a multicelled battery.