A slip of the tongue; saying something different from what one intended (a mistaken or inadvertent statement).
さっきの説明は言い違いで、実際には期限は来週でした。
That explanation earlier was a slip of the tongue — the deadline is actually next week.
彼の言い違いが原因で会議が混乱した。
The meeting got confused because of his misstatement.
ごめん、言い違いをした。明日は金曜日じゃなくて木曜日だ。
Sorry, I misspoke. Tomorrow is not Friday but Thursday.