noun
the big day; D-day; day when a major event is expected
Colloquial wasei-eigo from English 'X-day'. Used for an anticipated important day, often with a sense of countdown or speculation.
wasei-eigo (Japanese-coined English), from X-day
次の選挙のＸデーはいつになるか、みんなが注目している。
Everyone is watching to see when the big day for the next election will be.
彼女がついに引っ越すＸデーが来週に決まった。
The big day when she finally moves out has been set for next week.