Personality disorder not otherwise specified, also referred to as personality disorder NOS, is a diagnostic category in the Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV-TR). This diagnostic category is reserved for a clinically significant problem in personality functioning that does not fit into any of the other existing personality disorder categories.
Perhaps you do indeed have some of the symptoms of borderline personality (BPD), but not enough to meet diagnostic criteria. Or perhaps you have some symptoms of BPD and some symptoms of another personality disorder.
In either case, your provider may have decided that while your symptoms are not a perfect match for any existing personality disorder category, they are important enough to warrant a diagnosis of PD-NOS.
American Psychiatric Association. Diagnostic and statistical manual of mental disorders, 4th ed, text revision. Washington, DC, Author, 2000.