Yesterday (time)

Yesterday is a temporal construct of the relative past; literally of the day before the current day (today), or figuratively of earlier periods or times, often but not always within living memory.
Learning and language.
The concepts of "yesterday", "today" and "tomorrow" are among the first relative time concepts acquired by infants. In language a distinctive noun or adverb for "yesterday" is present in most but not all languages, though languages with ambiguity in vocabulary also have other ways to distinguish the immediate past and immediate future. "Yesterday" is also a relative term and concept in grammar and syntax.
Yesterday is an abstract concept in the sense that events that occurred in the past do not exist in the present reality, though their consequences persist. An often-quoted aphorism states something along the lines of "Yesterday is history, tomorrow is a mystery, but today is a gift. That is why it is called the present". The earliest version of this aphorism appears to occur in 1912, with the Frank M. Pixley quote, "Yesterday is history; to-morrow is merely a hope; to-day is the only absolute asset of time that is yours".
Some languages have a hesternal tense: a dedicated grammatical form for events of the previous day.