It’s taken me ages, relatively speaking, to link to Steve Cook’s post on getting rid of meta. In the meantime, though, he’s written my comment for me:
A metamodel specifies the concepts of the language in which the model is defined.
That seems to be about as clear as it gets, as opposed to this:
[…] we decided to call the models of the concepts in our DSLs Domain Models; which contain Domain Classes, Domain Relationships, Domain Properties, Domain Roles and so on. These models are used to generate tools, and serialized in files. We also have a model which we use to generate the tool and formats that we use to manipulate Domain Models – we call this the Domain Model Domain Model, or DMDM