Toum and aioli are alike in that they are both emulsions. Toum is an emulsion of garlic, salt, lemon, and a neutral oil and can be thick enough to use as a spread. Traditional aioli is an emulsion of garlic and olive oil, but more often is a garlicky mayonnaise. Mayonnaise is a version of aioli that also contains eggs. Toum is a traditional Lebanese garlic sauce. Aioli is a traditional European sauce from France and Spain.