A Boundary Class is a stereotype of a class that is specified in UML Extensions for Business Modeling. It can be shown as a regular class rectangle with stereotype of "boundary", or as the following special icon:

A "boundary class" is a class that lies on the periphery of a system, but within it. It interacts with actors outside the system as well as objects of all three kinds of analysis classes within system.

To draw a boundary class on a Use Case diagram, select the Boundary icon from the tools menu.

See also Changing from icon view to class view.