To admire greatly; to be deeply impressed or respectfully acknowledge someone's effort or skill.
あの先生の研究熱心さには本当に頭が下がる。
I'm truly impressed by that teacher's dedication to research.
君の努力には頭が下がるよ。よく頑張ったね。
I'm impressed by your effort. You did well.
彼はボランティア活動で多くの人を助けており、皆が頭が下がる思いだ。
He has helped many people through his volunteer work, and everyone admires him.