A text grammar is the study of texts above the level of the sentence. It shows how texts are put together so as to convey ideas, facts, messages, and fiction.
A similar term is discourse analysis. Both are mostly concerned with natural language use; discourse analysis would include spoken language. Speech is also the parent of rhetoric, the ancient study of persuasive speaking. In a similar way, literary criticism parallels text grammar, because both concentrate on the printed word. A text grammar approach puts emphasis on the linguistic structure of a text, rather than its cultural or symbolic meaning.
A text is a coherent body of sentences. Coherent means they are linked by a consistent theme. The text ends when completion is signalled. For example, when a problem introduced at the start is solved, or when a promised discussion has reached a conclusion.