"Personality Disorder Not Otherwise Specified" (PD-NOS) is a diagnostic category used in the DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition). However, it's important to note that the DSM-5 (Fifth Edition) has replaced PD-NOS with the term "Other Specified Personality Disorder" (OSPD) and "Unspecified Personality Disorder."
When a mental health professional uses PD-NOS or OSPD, it means that the person's symptoms and characteristics do not fit neatly into a specific personality disorder category outlined in the DSM. Instead, they might have some traits from different personality disorders or not enough symptoms to fit a particular diagnosis fully.
In your case, you mentioned that borderline personality disorder (BPD) was discussed. It is possible that your therapist noticed some characteristics or symptoms that are common in borderline personality disorder, but they might not fit all the criteria for a clear-cut BPD diagnosis. Hence, they used PD-NOS or OSPD as a more general classification.
It's crucial to remember that only your therapist can provide a definitive explanation of the diagnosis they assigned to you. If you have questions or concerns about your diagnosis or therapy, don't hesitate to discuss them openly with your therapist. Understanding your diagnosis is essential for your treatment journey, and they should be willing to clarify any confusion or doubts you have.