The definition of an omelette is scrambled eggs with a shape. Madame Poulard in her restaurant at Mont-Saint-Michel made omelettes famous. I’ve often thought that maybe what made them so good was the fact that the hens “grazed” on the salty marshes around Mont-Saint-Michel and the eggs got seasoned from within—just like the lambs raised in the salty meadows—but maybe not.
Omelettes may be made any size, but until you master the technique of the 2-3-egg size, don’t attempt the 8-10-egg variety. To my way of thinking the small ones are best since no part of them gets overcooked. Also, I prefer to have a whole individual omelette rather than one-half or one-fourth of a large one. Large-sized omelettes are hard to cook, to shape, and to prevent from having at least some small part of them overcooked and dry.