This is the 12782nd most frequent Korean word.
덜미를
"덜미를" refers to the nape of the neck or the scruff of the neck.
덜미를 here refers to the figurative 'back of the neck,' indicating the point of being apprehended.
도둑이 덜미를 잡혔다.
The thief was caught.
덜미를 directly refers to the physical back of the neck in this context.
그는 덜미를 다치고 움직이기 힘들었다.
He injured the back of his neck and found it difficult to move.
덜미를 metaphorically represents being caught or exposed for one's actions.