معنی کلمه :‌ folder

One who, or that which, folds; esp., a flat, knifelike instrument used for folding paper.

(a) Capable of being thrown or cranked in two directions, usually opposite to one another; as, a two-throw crank; a two-throw switch. (b) Having two crank set near together and opposite to one another; as, a two-throw crank shaft.