What exactly borderline personality disorder?

Borderline: Intense unstable interpersonal relationship characterized by idealization, splitting, rapid mood shifts, pan anxiety, repeated self harm, distorted self image, low esteem, brief psychotic episodes.

Bordeline PD: Personality disorders are enduring, inflexible patterns of inner experience ; behavior causing significant distress in relationships, work, ; other important areas. "borderline" applies to a person with unstable sense of identity; extreme fear of being alone; unstable relationships; impulsivity; affective instability; extreme anger; chronic suicidality or self-mutilation; mini-psychotic times.

A "hardware" deficit: There are brain subsystems that regulate the relationships between self-interests and interests of others. These systems can have hardware defects. These may result in "personality" disorders. BPD is one form of a disorder in these systems.

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.