Product designers have tools they use to define activities, tasks, actions, and operations such as activity diagrams, wireframes, and prototypes.
Activity diagrams divide the activities into tasks needed to complete the user’s objective. A task is a unit of work. The task itself may be a single step in the process or multiple steps or sub-tasks that make up the task. Activity diagrams, sometimes called process flow diagrams, divide the scenario tasks as needed to convey what the user needs to do to complete their goal.
Tasks analysis looks at tasks as outcomes that have actions. Actions usually result in some form of commitment. For example, selecting the “OK” button in a software interface or pressing a button on a device that results in a desired outcome. And an operation is the outcome of the user’s action. The operation is the program initiated and yields the results of the user’s intended goal.
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Van Tyne, Sean. Defining and Designing Technology for People. The Pragmatic Marketer, Volume 8, Issue 2, 2010