It is the set of rules, principles, and processes that govern the structure of sentences in a given language, specifically word order and punctuation. The term syntax<span> is also used to refer to the study of such principles and processes.</span>
The word <em>that </em>is used as a relative pronoun here, it can be interchanged with the pronoun <em>which, </em>and both are used to connect two parts of a sentence.