Scrum is a subset of Agile and is a lightweight process framework for Agile development. Which role becomes the interface between the business the customers, and their product-related needs on one…

The Product Owner is the Scrum role formally responsible for representing business and customer needs, translating those needs into a prioritized product backlog, and ensuring the team delivers the highest-value increments - making them the defined interface between the business side and the Scrum Team as specified in the Scrum Guide.

Program Manager is not a defined Scrum role and operates at a portfolio or program level rather than serving as the interface between customers and a specific Scrum Team.

The Scrum Master acts as a process facilitator and servant-leader who removes impediments and upholds Scrum practices, but does not own the product vision or represent customer and business needs.

Product Manager is an organizational title that may coexist with Scrum in some companies, but it is not a formal role defined in the Scrum Guide.