The first third of a month—the period roughly from the 1st to the 10th day; used to indicate part of a month.
会議は来月の上旬に予定されています。
The meeting is scheduled for the beginning of next month.
上旬は出張が多くて忙しかった。
I was busy with many business trips in the early part of the month.
上旬・中旬・下旬でスケジュールを分けて確認しよう。
Let's divide and check the schedule by early, middle, and late parts of the month.