* A postgraduate diploma in a related field: This could be a postgraduate diploma in clinical psychology, counseling psychology, psychiatry, or a closely related area. These diplomas are awarded after completing further study *beyond* an undergraduate degree. They represent specialized training in a particular aspect of mental health but are not a standalone qualification for independent practice in most jurisdictions.
* An older or less common qualification: In some older or less common educational systems, a diploma might have existed with a similar name. However, these would likely be superseded by more modern, standardized qualifications such as those mentioned above.
* A misleading or inaccurate title: The title itself could be inaccurate or used informally to describe a program that doesn't officially use that name.
To understand what someone means, you'd need more context. Ask them to clarify the institution that awarded the diploma and the specific title of the qualification. This will provide a much clearer understanding of the training involved.