Is the statement of the person who accused the girl of misconduct considered an accusation of unchastity (qadhf) or backbiting (gheebah), and what is the ruling on such an act?

If a man describes a woman with a bad characteristic that is not present in her, then it is slander (buhtan), which is more forbidden and sinful than backbiting (gheebah). He must repent to Allah, and seek forgiveness from the woman if she became aware of what he said about her. Otherwise, he should suffice by supplicating for her and praising her well in front of those before whom he slandered her. If he accused her of committing indecency, that would be an accusation (qadhf) and backbiting. However, if he did not accuse her of indecency, it is not considered an accusation (qadhf), but it is a serious crime and a major sin.