The term syntax comes from a Greek word meaning "arrangement together." Essentially, syntax refers to the rules by which sentences are constructed (regarding specific languages). For example, in French, most nouns are "gendered" (meaning that a la (feminine) or le (masculine)). "Le" and "la" are articles (like "the" in English) which must precede the noun.
In a Standard English sentence, examples of syntax are as follows: subject/predicate; noun, verb, object (noun); or article, noun, verb.
Jane Austen, in many of her novels, typically uses standard syntax. That said, in the opening sentence of Pride and Prejudice, Austin uses a very different type of sentence: "It is a truth universally acknowledged, that a single man in possession of good fortune, must be in want of a wife." Curiously, the sentence (when punctuated as it is) consists of nothing but fragments.
Here, her syntax is correct, yet the sentence may seem drawn out to the modern reader. Given her formal education, Austen's syntax was very formal. In some cases though, Austen changes the standard syntax of a sentence. For example, "This was invitation enough" should read "This invitation was enough." The movement of the verb before the noun makes the sentence far more powerful. If Austen strays from standard syntax, she does so for a good reason and purpose.
Overall, Austen uses different styles of writing to accentuate specific aspects of each of her novels. Pride and Prejudice focuses upon dialogue; Northanger Abbey plays upon parody and the vague. She plays upon the word "comfort" in Mansfield Park, and Persuasion is satirical (a break from her normal style).