Alistair Cockburn pointed us to an excellent article by Melissa Perri about the differences between a product manager and (Scrum) product owner. The article clarifies some confusion. I’d like to repeat and emphasize some points that have been omitted (and where I also disagree).
Foremost, a product manager works on products for a market (i.e. many customers). I have never seen a product manager work on a project with one customer. For a product owner this is undefined; they could be working on a product for a market or on a project for a specific customer.
Also, in my opinion, a product manager and product owner always have contact with their market and customers. The idea that a product owner should only be writing user stories, without talking to users of the software ever, seems really foreign and sad to me.
Finally, a product manager can either be a strategic or a technical product manager, where the strategic PM often is the superior to several technical PMs. The strategic PM is responsible for the product vision and roadmap, while technical PMs are responsible for the detailed requirements. This way, you can tackle a large product or product line or product portfolio in a coherent way. There is no such thing in Scrum like a strategic vs technical product owner.
With this, we can define a Scrum product owner to be a technical product manager for a product for a market. It thereby covers a particular niche of product management.