An OTF knife is a knife whose blade extends and retracts from an opening at the front of the handle. When retracted, the blade is hidden within the handle. When the blade is extended “Out The Front,” it’s locked into place. It then cannot be pushed back in toward the handle except by either a retraction lever at the top or side of the handle. This action is considered to be dual action when the slider, which is pushed forward by the thumb to extend the blade, can be pulled backward by the thumb, retracting the blade.