A playlist is a collection of activities, resources, and assessments.  They can be complex enough to cover all the standards in a level, or smaller and targeted enough to help students demonstrate mastery on past content and fill learning gaps.  When students are assigned a playlist, Empower will automatically identify those activities and quizzes that the student will not have to complete.  The only activities and quizzes that are able to be skipped by students are those that contain standards that have already been mastered by the student.