Predefined Variables
Flow Designer automatically creates predefined variables when you use certain events and activities in a flow.
A list of the available predefined variables appears in the Predefined Variables section in the Global Flow Properties pane. They also appear in the Properties pane for the selected Event or Activity.
Click on each variable to open a pop-up window that explains what type of data the variable stores, so you know how to use the variable in your flow.
While most attributes of an Event Output Variable are predefined and cannot be edited, you can edit the variable to modify the global variable designation.