A Technical Standard Order (TSO) is a minimum performance standard for specific materials, parts, and appliances used on a civil aircraft.

A Parts Manfacturing Approval (PMA) is a combined design and production approval for modification and replacement articles for use on a civil aircraft.  A PMA appplication requires identification of the product on which the article is to be installed into. That typically requires a Supplemental Type Certificate (STC) to show that the design of the article meets the airworthiness of the aircraft it is being installed into.  

The TSO allows the article to have broad installation possibilities. As a modificatiion and replacement article, the PMA article is designed for installation limited by the STC.