I'm curious as to what precisely is borderline personality disorder?

Borderline PD: It's a b cluster personality disorder (dramatic, emotional or erratic). Individuals show marked impulsivity and instability of - mood, interpersonal relationships, and self image. Often seen in young adults, it can be very dangerous as fluctuations of feelings toward others ; self are extreme ; intense. Life is difficult for the person ; everyone around them. Love/hate - on/off.

Borderline: Intense fear of abandonment, being manipulative, impulsivity, a tendency to think of people and things in all good or all bad terms, self mutilating behaviors, drug and alcohol abuse, sexual impulsivity, a profoundly disturb sense of self, and extreme emotional volatility.