The day immediately before today; one day ago. / (figuratively) The past, often in terms of being outdated.

On the day before today. / (informal) As soon as possible.

plural of yesterday.

(informal, chiefly in the negative) To be new, naive, innocent, inexperienced, or easily deceived.

(idiomatic) To need something immediately or urgently; to need something that is already late.

Last night.

Something now irrelevant.

It is impossible to change or to relive what has already happened.

Alternative form of yesterday is gone

(regional) day before yesterday