The metamodel in the case of use case maps is the model that represents use case maps. The model in terms of JUCMNav is an abstraction used to to represent code that encapsulate the use case maps logic at the code level. When thinking of metamodel think of the class diagrams of ucm, urn and grl. When thinking of model, think of the Model View Controller pattern in jUCMNav.
These two terms are so frequently used that, if they are interchanged, they risk confusing a newcommer who cannot yet extract the correct meaning from the context.
-- JordanMcManus - 11 Jul 2005