九月九日忆山东兄弟

山东 here is not Shandong province. In Tang usage it meant the land east of Mount Hua (华山), where the family of 王维 lived, in today's Shanxi. On the Double Ninth people climbed hills and wore sprigs of dogwood (茱萸) against bad luck, which is why the poem ends 遥知兄弟登高处，遍插茱萸少一人 'far away, I know, my brothers have climbed the heights, all wearing dogwood, and one of them is missing'.

Its first couplet, 独在异乡为异客，每逢佳节倍思亲 'alone in a strange land, a stranger, at every festival I miss my family twice as much', is quoted by anyone who spends a holiday far from home.