The following are based on my experience in TKD. YMMV. 


PUNCH

WHAT: A punch is a closed fist technique usually delivered in a linear fashion.It is used in attacking, counter attacking, and defense depending on the situation. 

TYPES:  Horizontal & vertical. The two large knuckles or all four are used. Boxing type hooks and uppercuts are also used in some TKD styles where knuckle positions are between a horizontal and vertical punches. However, unlike boxing, the backhands of the fist are also used.(i.e. back of the fist punch). Other punches(high uppercut, obverse twisting punch, double horizontal, simultaneous high & low, knuckle protruding, etc) are also taught in black belt(1st degree & up) curriculums of TKD.  These punching techniques are not usually  found in the color belt curriculums.  This leads many people who only have short experience in TKD to criticize the lack of hand techniques in TKD.

POWER for the punches are generated from the torso and the waist. In some instances the power is also generated from the propulsion from a foot or both feet pushing forward. The twisting by ball of the supporting foot or both feet are also applied. In addition, there is an up & down knee movement called the “sine” wave in ITF to generate power.

IMPACT DELIVERY: 
Either “push through” where the punch goes beyond the target or the “whip crack” where the punch is stopped at the point of impact.

DELIVERY PRINCIPLE: Action-reaction(Newton’s third law of motion). A combination or flurry of punches works much more effectively than a stop action single punches. A fast action-reaction principle is applied here.  Energy retained from a quickly pulled back punch is transferred to the other arm to propel the opposite punch.

TARGET:
General area(on Head/Face, upper torso, under chin, etc.)

APPLICATION ANALOGY:  A large hammerhead hitting a large surface area. 


STRIKE

WHAT:  Open or semi open hand techniques delivered in a CIRCULAR motion to increase speed of the  delivery thus more impact. Circular closed fist techniques are also included as well as head butting(forward or
backward)techniques.

TYPES:  Hand and arm techniques, backfist, curved wrist(kok kwon), spinning back fist variations, open palm, open curved hand(index and thumb are opened), knifehand variations, elbow variations(up, down, side, back, back turning), arm bars, & others.

POWER for the strikes are generated by twisting or winding up of the torso and the waist plus the acceleration by the arm/hand. Footwork plays a crucial role in turning the body around 180, 270 or 360 degrees in combinations. The footwork and winding of the waist is important in accelerating the strike to deliver power. Acceleration helps the flow or transition in single or multiple counter spins. Immediately after one circular strike, a same or different circular strike comes from the opposite direction with the opposite hand) for both power and the surprise element.

IMPACT DELIVERY:
  “Whip crack” where the force is stopped at the point of impact after circular  acceleration.  To a lesser degree, “push through” is used as well.

DELIVERY PRINCIPLE: Circular motion in an arc.  A car needs distance to accelerate. When water ski and boat is going at the same speed, the water ski making an arc to the side will accelerate by covering more distance. The ski will eventually go faster than the boat.  The same principle is applied in strikes. The small rotational spin of body allows a larger distance covered by the outer body extremities-knifehand, backfist, arm, or striking elbow and can deliver a powerful hitting force. The strike may come from the top-down/down-up
in an arc in a vertical plane or from the side in horizontal plane. Experienced martial artists will use arcs in any geometrical plane. Effective open palm strikes are linear plyometric strikes. However, palm strikes can also be
delivered in an upward circular strike to the face or body.

TARGET: A specific pressure/vital point is targeted with a fast single circular
blow for immobilization. Specific targets on the face(eg. in-joong, jaw
joints); neck(eg. wind pipe, artery); on the body(eg. floating ribs, sternum);
various pressure points on the arm; certain points on the spine, skull, etc.

APPLICATION ANALOGY:  A small hammerhead swung with a high speed in an arc onto a small defined area.


THRUST    

WHAT:  Usually hand and sometimes foot technique.  Linear delivery is involved.


TYPES:  Knife hand tip thrusts to the neck and solar plexus. Twin finger thrusts to the eyes.  Palm thrust to the target sometimes going beyond the outer body layer to impact inside the body.  Pushing kicks to neutralize or attack by targeting attackers pressure points, etc. 

POWER GENERATION:  Generated from the waist, torso, and twisting on the ball of the foot.  Also from the momentum created by  the whole body pushing off with one or both legs.  Sometimes simply shifting the angle or a slight in step of the supporting foot for thrusting-in effect.                

I
MPACT DELIVERY: Two main types.  A “whip crack” OR a “push off”.  Both are used depending on situations.  The third type is a combination of the “whip crack” AND a “push through” that comes from experience and training.

DELIVERY PRINCIPLE: First type is a plyometric type linear attack(whip crack) to a small specific pressure point as in a knifehand thrust using variety of finger tip techniques. Examples are thrusts to the solar plexus (middle section on the sternum), to the neck(section just below the Adam’s apple), or to the pelvic bone(low section to the center of the pelvic bone plate). 

Second type is to push off an incoming attack or attacking a narrow target. This is done either with a foot or hand technique. Example would be intercepting and neutralizing movements(such as kicks of hard styles or
circular takedowns of soft styles).  The push/thrust in the counter technique makes it much more effective.

The third type requires an extra “thrust” to the narrow target area by combining “whip crack” AND “push through”.  This can be applied in both hand and foot techniques.  Highly experienced martial artists use this
thrusting technique instinctively by extra digging in/shifting/angle adjustment of the supporting foot and/or the body plus timing.

An example of the third type is what you often see in promotion tests. There the first board is intact and the second or third  board is broken inadvertently by a white or yellow belts(alas, sometimes by upper belts as
well). Most BBs trained under a good instructor or GMs know the details of delivering this technique. The GM will sometimes train the high ranking belts in refining this technique. However, in the U. S. most will not teach the technique due to legal implications. 

TARGET:  A very narrow specific point on the outside or inside the body.

APPLICATION ANALOGY:  A small hammerhead hitting directly on a nail head with one and a half blow(the half is almost simultaneous) for deeper penetration OR to strike a target that is below the nail. The nail head transfers the energy.  There is a subtle difference here in delivery of the two.
ARTICLES
The Difference between a Punch, a Strike, and a Thrust
by W Rhee
ARTICLES
The Difference between a Punch, a Strike, and a Thrust
by W Rhee