Open-hand strikes include various techniques used in the martial arts

Martial arts

Martial arts are extensive systems of codified practices and traditions of combat, practiced for a variety of reasons, including self-defense, competition, physical health and fitness, as well as mental and spiritual development....

 to attack or defend without curling the hand into a fist. The most famous of these techniques is probably the so-called "karate chop", which is also described as a knife-hand strike (shuto uke) although there are many other techniques.

Some of these are:

1. techniques that use the edge of the hand closest to the little finger or use the opposite edge of the hand: A knife-hand strike may be delivered along an arc somewhere midway been vertical and horizontal, usually with the aim of numbing an attacker's forearm.
2. techniques that use the other edge of the hand are more difficult to execute since care has to be taken to position the thumb so that it will not be injured. Performing this move in a way that is powerful will generally involve striking with the palm facing down. And so doing will mean that, e.g., the person using this strike will attack the left side of his opponent's body with the right knife hand, or vice-versa.
3. spear-hand attacks are performed by keeping the extended fingers tightly compressed together and thrusting directly into some target of relatively small diameter, such as the throat. In many types of karate it is referred to as a "nukite".
4. the back of the hand, with the fingers loosely curled, can be used in an upward-arcing strike to the groin
   Groin
   In human anatomy, the groin areas are the two creases at the junction of the torso with the legs, on either side of the pubic area. This is also known as the medial compartment of the thigh. A pulled groin muscle usually refers to a painful injury sustained by straining the hip adductor muscles...
   
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5. the cupped hands can be used in unison to attack the ears, potentially damaging the opponent's eardrums.
6. the heel of the hand can be used to strike a target without fear of damaging the knuckles. This is referred to in Okinawan styles as a Teisho or Shotei strike.

One of the greatest advantages of an open-hand strike is the ability to quickly grab the opponent to perform a follow-up, such as a throw or a pull into another strike. The extra control this affords as compared to a punch is worth the larger risk of damage to the hand or fingers.