excellent calligraphy; skillful writing
Refers to calligraphy of high quality, or the skill of writing beautifully. Often used in contexts praising someone's handwriting or brushwork.
I am always impressed by his excellent calligraphy.
この掛け軸は能書の見本のような作品だ。
This hanging scroll is a work that exemplifies skillful calligraphy.
Compound of 能 (skill, ability) and 書 (writing, calligraphy). The exact historical derivation is uncertain, but the meaning is transparent from the components.