An Empty activity denotes an activity with no action to be performed. You can specify the Name and Description, but there is no input or output for this activity.
This activity is useful if you want to join multiple transition flows. For example, there are multiple transitions out of an activity and each transition takes a different path in the process. In this scenario you can create a transition from the activity at the end of each path to an Empty activity to resume a single flow of execution in the process.