Overrides let you take over a playlist on a temporary basis. The change is immediate. Any content from Telemetry (Media, Board or App) as well as a textual Alert or Informational message can be used as content for an override. Only one piece of Content can be displayed as an override at one time.
Scheduled overrides occur during a window of time, letting the content take over screens during that window and being removed when the window ends.
Manual overrides start out paused and you must manually un-pause them to apply the override. This is useful for someone to predefine overrides that they play to use in the future and have the design and message setup but are then available for quickly unpausing when needed.
Recurring overrides will be shown repeatedly on an interval and duration specified by yourself. They are useful for placing messages that must be shown on a regular recurring basis.