before bottled mayonnaise was common, home cooks made a "salad dressing" that looked like mayonnaise, but it was a boiled dressing made with vinegar and flour, sugar, cream, salt, I think that was all. It was served on salads - those composed salads of yore, made with some ice berg lettuce, an egg, maybe half a canned peach, or a square of jello on a leaf of lettuce with a dab of boiled dressing, you know the sort of thing. That's where Miracle whip comes from - boiled dressing - and that's why it is called salad dressing, although I think the only salad people use it on nowadays is potato salad (too sweet for tuna salad.) I was raised on Miracle Whip and love the stuff but it gives me indigestion now, and regular mayo is too high in calories.