Abstract Element refers to a place-holder for a UI element that an action logic needs to interact with. In a fast paced agile environment, you may not always have access to application UI when you are developing automation test logic. It is possible that development team is still working on the UI development or the application environment may not be stable enough to support continuous access.
You can either create an abstract element explicitly from the element repository by clicking on "add abstract element" or more contextually when you are developing action logic.
For an existing statement or when creating a new statement in action logic, you can contextually create an abstract element for an argument that expects a UI element. Provide a meaningful name and select the type of element. Optionally, if the synch element is not yet setup for the Context, you are required to select if this new element should be marked as synch element.