Yes zen you were right it's the border of neurosis and psychosis.

The term "borderline" is a misnomer. These patients were first described sixty years ago by psychoanalysts who noted they did poorly in treatment, and therefore theorized that this is a form of pathology lying on the border between psychosis and neurosis.

Here's the link to that article.
http://www.jwoodphd.com/borderline_p...y_disorder.htm