It is a large Krabby Patty that is double batter fried and served on a stick.
Role in episode
Harold orders a King-Size Ultra Krabby Supreme with mayonnaise at the beginning of the episode. He thanks Squidward for the order, who calls him a "barnacle head." Harold walks back up to him to hear what he just said, and Squidward says that he forgot his mayonnaise. Harold thanks him again and then proceeds to eat the patty and squirt the mayo in his mouth. Squidward expresses disgust for the way Harold is eating his food and then openly admits his distaste for Krabby Patties.