It was originally a local term for cell phones batteries, because smart phones batteries are bulky (i.e. board shape), so they are called like this. Usually the electric
board is electrical appliances, circuit boards and so on. The FPC harness is smooth and flat in strip shape, very thin in thickness, and its width can be customized
according to the size of the battery pack. FPC harness and battery pack are tightly integrated, no gap, which can save a lot of space.