noun
opening; beginning; commencement
Literally 'lid opening', used figuratively for the start or opening of an event, project, or period. Often implies the initial stage or the moment something begins.
新年度の蓋開けは来月だ。
The opening of the new fiscal year is next month.
プロジェクトの蓋開けに立ち会った。
I was present at the commencement of the project.
Compound of 蓋 (futa, 'lid') and 開け (ake, 'opening'), from the verb 開ける (akeru, 'to open'). The figurative sense of 'beginning' comes from the image of opening a lid to reveal or start something.