noun
past misdeed; past error; past folly; past sin
Refers to one's own past wrongdoings or mistakes, often in the context of repentance or reform. Common in the set phrase 前非を悔いる (to repent of one's past misdeeds).
彼は前非を悔いて、心を入れ替えた。
He repented of his past misdeeds and turned over a new leaf.
前非を改めることが大切だ。
It is important to correct one's past errors.