What Is a Chunk Shot in Golf?
Chunk used as a noun applies to that outcome: hitting behind the ball, the ball not going very far. "Dang it, I just hit a chunk shot." Chunk used as a verb applies to the act of producing such a shot: "I chunked that one pretty bad" or "be careful not to chunk it."
The most common term for chunk shots is "fat" or "fat shot." A chunk shot and a fat shot are the same thing. "Chili dip" is another common slang term for this shot. Perhaps the original golf term for a chunk was "sclaff," rarely used today.
In the chunk shot, the golfer's club strikes the ground behind the golf ball, contacting the turf before contacting the ball. With an iron, this usually results in the clubhead digging into the ground, resulting in turf coming between the clubface and golf ball, further killing the momentum of the shot. A chunk usually digs up a lot of turf. Basically, when you chunk it you are stubbing your golf club.
The term probably originates from the chunk of turf that often goes flying on chunk shots.
Here is a video that goes into some of the most likely causes and fixes for chunk shots:
You can find many more tutorials on correcting this mishit by searching YouTube for chunk shot or fat shots in golf.