expression, noun
that day; the very same day
Refers to a specific day previously mentioned or understood from context. Often used in narratives or when recalling a particular day.
その日は朝から雨だった。
It was raining from the morning that day.
彼に会ったその日に決心した。
I made up my mind the very day I met him.
あの日 also means 'that day' but carries a stronger sense of distance or nostalgia, often referring to a memorable day in the past.
この日 means 'this day' and refers to a day close to the present or the day being focused on in a narrative.
Compound of その (that) and 日 (day). A straightforward demonstrative-noun phrase.