Common Ground refers to the CommonKnowledge of the context of an instance of language use. I am using common ground the way Herbert H. Clark defined it in "Using Language". Consider what he says in this paper on Reference Diaries.
"When we make a definite reference to a thing, we normally make sure that our audience "shares" with us certain knowledge about that thing. To refer to a woman as she, the woman, or Nancy, we usually have good evidence that our audience knows about her too. But exactly what "shared" knowledge is required? This question is critical if we are ever to discover how people make or interpret definite reference--how they represent knowledge in memory and consult it in uttering and interpreting expressions like she, the woman, or Nancy. The question is critical if we are ever to characterize the mental archive people have for storing the facts they need to know for definite reference. We will argue that this archive has to be another detailed diary, or reference diary, supplemented by atlases, histories, and certain other reference texts. To make this argument, and to see what goes into the archive, we will examine the prior question, What "shared" knowledge is required for definite reference?"
And this points out a new way to look at the idea of context for use in the semantic web of data. These suplemental materials that Clark describes above, a reference diary, atlases, histories, and other reference texts, can be just so much more RDF data. But it should structured, and should often apply to single RDF statements.