Correction or revision of writing, answers, etc.; reading over and improving or fixing errors (often done by a teacher or reviewer).
先生に作文を添削してもらい、表現を直した。
I had my composition corrected by the teacher and revised the expressions.
模範解答と照らし合わせて答案を添削する。
I correct the answers by comparing them with the model answers.
添削した箇所に赤で印を付けて返却した。
I returned it with the corrected parts marked in red.