This is a variant of the Parallel component. The essential difference is that this is a "partial" model. It is therefore not allowed to drag it. The only purpose of this model is to inherit from it in order to construct a new model that is a special Parallel component.
The Figure below shows a component ("s2") built from a PartialParallel component. As the diagram and the icon layer of the PartialParallel component does not need to be the same size, the user can benefit from collecting large subsystems in smaller closed Parallel components to improve overview and modularization of the full system.