During the morning; the time period from morning until noon (before midday).
明日の午前中に病院へ行きます。
I'll go to the hospital tomorrow morning.
午前中は会議があるので午後に来てください。
I have meetings in the morning, so please come in the afternoon.
この薬は午前中に飲むと効果が出やすい。
This medicine tends to work better if taken in the morning.