Gobbledygook is unintelligible nonsense, often a bunch of big words that you can't comprehend. The mechanic might try to explain what's wrong with your car, but to you it just sounds like gobbledygook.
Like gibberish, gobbledygook is essentially meaningless to the person listening to or reading it. What distinguishes gobbledygook is that it includes technical terms or overblown, complicated words that aren't necessary. A good editor will take a technical writer's gobbledygook and translate it into ordinary English that anyone can understand. The inventor of this term was a Texas politician who used "activation" and "implementation" as examples of gobbledygook.