Mayonnaise is a thick, creamy sauce or dressing that is made of oil, egg yolks, lemon juice or vinegar, and seasonings. It's not the same as salad dressing, which doesn't contain egg yolks and is generally sweeter than mayonnaise.
I've enjoyed Thousand Island salad dressing for years, and I've always wondered how it got its name. For that matter, how did ranch dressing get its name? Is French dressing really from France? And what is in those dressings?