「昨日」 means yesterday, referring to the day before today. This word is essential for discussing past events or experiences from the previous day. You will often use it with past tense verbs.

「今日(きょう)」の一つ前(まえ)の日(ひ)を意味(いみ)します。昨日(きのう)あった出来事(できごと)や過去(かこ)の経験(けいけん)を話(はな)すときに使(つか)います。