noun, adverb
the day in question; that day; the day of
Refers to a specific, previously mentioned or contextually understood day, such as an event, appointment, or deadline. Often used adverbially without a particle.
試験当日は早めに会場に着いた。
On the day of the exam, I arrived at the venue early.
チケットは当日会場でお求
Please purchase tickets at the venue on the day of the event.