The Product Owner (PO) role comes from the Scrum methodology, though it's now used beyond
classic Agile. A PO represents the interests of the users and the business inside the development team.
If the PM is thinking about what to do next year, the PO decides what the team will do in the next sprint.
The PO lives inside the dev process: they detail tasks, explain exactly what needs to be done, check the results, and say "done" or "redo." They are maximally accessible to the team – developers need to be able to ask questions and get answers fast.