Folding knives have a blade that can be safely stored inside the handle and rotated or extended in to the 'open' position for use. These knives are easy and safe to carry inside your pocket and they are useful for a wide variety everyday cutting tasks, but they are generally not recommended for heavy duty cutting tasks or use as a pry bar.
Folding knives can be separated in to two distinct types: 1) locking knives (e.g.: Frame lock, liner lock, back lock / lock back, button lock, bolt lock) and 2) non-locking knives (e.g.: Slip-joint, friction folder). Locking knives are generally safer to use because the blade can be locked in the open position.