This modification was justified as cost-effective because the scrambling algorithm was already used by the standard used to transport ATM cells over SONET/SDH.
The most important application of POS is to support sending of IP packets across wide area networks.
Cisco was involved in making POS an important wide area network protocol.
PMC-Sierra produced an important series of early semiconductor devices which implemented POS.
Given this information, POS technically stands for "Packet over Synchronous Optical Network/Synchronous Digital Hierarchy".