A Product Owner is a member of an agile development team. They are responsible for defining ‘what’ gets built, and for maintaining a prioritised and refined backlog of user stories.
I’ve been a Product Owner for about 3 years now, having migrated from working as an IT Business Analyst. The roles and skills required aren’t that different, but the agile way of working enforces a rigor to the quality of written requirements.
It also helps that the Product Owner is embedded in the development team, and is able to ask and answer questions to clarify exactly what’s required. And with agile I can respond quickly to changing priorities of the business.