What Are the Scrum Roles Again?

According to the Scrum Guide, Scrum teams have just three roles: Scrum Master, Product Owner, and Development Team.
The Scrum Master is in charge of the Scrum process, making sure the Product Owner and Development Team use the Scrum meetings effectively and protecting the Team from outside influences during sprints so they can complete their commitments. Agile Faculty can serve as Scrum Masters for their students in class and research settings, helping them to use the process to collaborate successfully and learn as the project continues.
The product owner is a link between the business and the Development Team. The Product owner is in charge of keeping the product backlog current and appropriately prioritized and helping the Development Team understand what users want to be able to do with the functionality they create. Agile Faculty can serve as product owners on committees, in lab or other collaborative research settings, and in client-based student projects.
The development team is composed of three to nine people who have the skills and knowledge to complete all the work committed to during a sprint. On a software team, this would include developers, user experience engineers, quality assurance testers, etc. In an academic setting, the team might be the members of a committee or task force, students completing a client- or community-based project, and researchers working together on a larger project.