필력이 · 필력을
writing skill, the power of one's pen
Example
그 작가는 데뷔작부터 탄탄한 필력을 보여 주었어요.
That author showed solid writing skill from the very first book.
Word parts
필 brush+력 power
Literally 'brush power' — how forcefully and skillfully someone writes.
Good to know
ㄹ + ㄹ is pronounced as a clear double L: [필력], pillyeok.