A Scrum Master is a coach at organization level.
A Scrum Master is a coach who coaches the development team in executing Agile practices to complete the work the Product Owner prioritizes.
He/She coaches the Development Team to create high-value products.
In addition, he/she coaches the Product Owner about managing the Product Backlog to facilitate empiricism-based product planning and arranging the items so that the order can maximize overall value.
Keep in mind: the Scrum Master ensures that goals, scope, and product domain are understood by everyone on the Scrum Team.