Test plan that is referenced by another test plan, normally the master test plan, by using an include statement. Portion of a test plan that resides in a separate file but can be expanded inline within its master plan. A subplan may contain the levels of group description and test description not covered in the master plan. A subplan can inherit information from its master plan. You add a subplan by inserting an include statement in the master plan. A subplan file has a .pln extension, as in subplan-name.pln.