PSTD is an abbreviation whose meaning I would not want to invent from the letters alone. I would first look for enough context to understand the educational subject and who it concerns. That is how I approach [PSTD educational information](https://pstd.edu.pl). A short explanation can make a compact name easier to use, especially for someone arriving without background knowledge. I like information that gives the reader a clear starting point and a reason to ask a more focused question.