A Ridgehand Strike (also sometimes called a Reverse Knifehand Strike) is a strike made with the thumb-side of the open hand (i.e., the ridgehand. In contrast, a strike made with the muscled-side of the open hand is called a Knifehand Strike. The thumb is tucked into the palm. The striking surface is the side of the first knuckle of the index finger.
Typically the striking arm is brought inward in an arc to strike, so that the palm is facing downward during the strike. In this case, the strike is called an Inward Ridgehand Strike or a Ridgehand Front Strike. If the word Inward is omitted, the strike is usually assumed to be inward.
The strike can also be made outward, palm-up however, with the hand moving from either the opposite waist or the opposite-shoulder, moving outward to shoulder-height; this movement of course would be called an Outward Ridgehand Strike.
This outward motion is more commonly used for blocking however, such as with the Middle Ridgehand Block in the form Joong-Gun. In this form, the chambering occurs by starting the ridgehand at the opposite shoulder, not at the waist; both arms cross in front of the chest to chamber.