Difference between activity and utility?

ANS: An activity is an instance of the Rule-Obj-Activity rule type. An activity is the fundamental sequential processing unit of the Process Commander system.

The shape in a Visio flow diagram, references an activity that updates a work object, but does not require user interaction and input. Your system includes standard activities for utility tasks, and you can create additional ones.

Each utility task references an activity with an Activity Type of Utility ss from utility shape  we can call activity but vise versa not possible.