This is the 14074th most frequent Korean word.
머리카락이
"Hair" (on the head).
머리카락이 is used as the subject of the sentence, emphasizing the action of the hair moving.
그녀의 긴 머리카락이 바람에 흩날렸다.
Her long hair fluttered in the wind.
Here, 머리카락이 indicates the subject (hair) that is in the state of being wet.
머리카락이 젖어서 드라이기로 말려야 해요.
The hair is wet, so I need to dry it with a hair dryer.
In this context, 머리카락이 serves as the subject of an event where the hair becomes tangled.