What are backbiting (gheebah) and slander (nameemah), and is mentioning details of one's life to others considered one of them?

Backbiting is your mention of your brother with what he dislikes, and it only occurs by specifying the person being spoken about or by the listeners knowing him. As for speaking about an unknown person, it is not considered backbiting. As for calumny (namima), it is the act of instigating discord and animosity by conveying words between people to corrupt their relationships. It includes revealing a person's secret that they dislike being disclosed, and anything else about people's affairs that one dislikes being revealed.