Many a times, with rich navigational capabilities on web applications, an Action may be applicable in multiple Contexts. In such cases, you can define the Action in one Context and share it with other applicable Contexts hence avoiding duplication of logic. When you are building Scenario workflow, this Action is available in all the shared Contexts. For all practical purposes there is no distinction of which Context the Action is actually defined. However, dependent resources for the Action such as Element defintions, called Actions etc. are expected to be maintained by the “owner” Context. At runtime, all the shared Contexts must have these dependencies available, so that the Action logic can run smoothly.
You can share an Action from the “Available From” tab of the respective Action sidebar.