Sources are data that is used to send to Outputs. Outputs then delegate this data to Layouts, which in turn process it based on Component configurations and render this data to the screen.
Media files - Slides/Announcements, Images, and Videos
Program
Calendar
Idle from the Idle Layout. This source type doesn't have explicit data. Idle buttons will send Idle(empty) signal to the Output, which in turn will be displayed (trigger) Idle Layout.