“Product Manager” and “Product Owner” to a great extent treated as same, which in my humble is not the case.
Product Managers often thought of as sitting at the intersection of business, design, and technology. They observe the market, what the customer needs, what competitors are up to and translate all this towards the product vision. They put a lot of efforts to prepare the vision for the product and to liaise with both internal (such as development/delivery teams) and external stakeholders (such as customers, sales/marketing, finance, management). As the advancement and the complexity of solutions/products is increased it has become very challenging for a Product Managers to balance it all.
Here come the Product Owners with helping hands. So, Product Managers don’t sit alone at that intersection, they are accompanied by Product Owners.
Product Owners take up all the internal stakeholders and the externals stay with the Product Managers. Together they manage all the stakeholders and make sure the product adheres to the vision.
This point onwards Product Manager put the entire focus to deal with external stakeholders and make sure what needs to be built. Product Owner takes that vision and works closely with development/delivery teams to make sure the product vision translated correctly to the end solution. Product Owner translates the vision into detailed requirements, create product backlog, prepare and priorities the features/functionalities in the form of easy, aptly sized, understandable user stories for a development team to carry out further work. Product Owners ensure what needs to be done first and what can be pushed for later. They constantly groom the backlog. They decide the acceptance criteria and accept the work done by the team. For the development/delivery teams, they work as a customer with the additional trait of empathy. Often Product Owners roles are best suited for the individual who has previous experience as a business analyst, consultant or Subject Matter Experts in the similar industry.
In theory, it is best to have both Product Manager and Product Owner working in tandem to run Product Management in an organization. However, on the ground, most of the organizations have one role which expects to play both Product Owner and Product Manager at the same time, which is hard to pull off and significantly impact the outcome (not just the output) of Product Management. Perhaps this practice could be justified and make more sense in a small size organization or a startup who always have to deal with limited resources. But bigger and established organization should take a step further, put more thoughts and efforts to streamline their Product Management function. And it begins by really understanding the difference between Product Managers and Product Owners.
In simple words, Product Manager’s role is more strategic where Product Owners are more tactical.