Syntax is an author's sentence structure. It is how things are phrased, and how correctly the sentence is formed. Broken grammar rules and disjointed wording would contribute to bad syntax, like if I was to say: "Grammar that's broke is bad syntax and wording out of order is too, bad syntax I were to mean." < -- THAT is atrocious. It's really bad. Syntax is what we say when we refer to the making of a sentence. There are all kinds of ideas, and the way we put them in order in a sentence matters. Good syntax leads to cleanly written and clearly understandable ideas.