Product Owner
The product owner is one of the roles defined in the scrum framework. The other roles are the Scrum Master and the developers.
In general, he is someone that has a really good understanding of the business, organization, and market. He represents the users and other stakeholders on the project. Consequently, his responsibility is to have a vision of the functionalities of the product that add value to the organization and to communicate those functionalities to the team. This responsibility is achieved by keeping a product backlog. A product backlog is a prioritized list of the product requirements.