noun
old days; former times; bygone days
Literary or formal term for the distant past, often with a nostalgic or reflective tone. Not used in casual conversation.
昔日の面影はもうどこにもない。
There is no trace left of the old days.
この町には昔日の繁栄をしのばせる建物が残っている。
Buildings that recall the prosperity of bygone days remain in this town.