When an event planner creates a new event, they can mark the event as 'Private' during the creation process. The event planner can also change an existing event to make it private. Private events will not be displayed on the Public Calendar but they will be displayed in all other areas of the system.
On the last screen of the 'Add New Event' process, there is a checkbox that marks the event as private (see image below)
After opening an event, press Change Event and select or unselect the private event checkbox (see image below)