There are different kinds of spreads; these derive from either animal fat or plant oil. What we refer to colloquially as butter is the stuff churned from cow's milk, and it is 80 percent fat. Milk is churned, separating the butterfat and buttermilk and the final product is tasty, but contains cholesterol.
Margarine is not a dairy product. It's produced from vegetable oils, and while margarine also has an 80 percent fat content, it doesn't contain cholesterol.
Butter is made from animal milk and is a dairy product. Margarine is made from vegetable oils, and is a vegetable product. Both butter and margarine, in a pure state, are gluten free. But additives are deceiving, so if you're buying butter or margarine, check the label.
Both butter and margarine are considered spreads. To market these spreads as butter or margarine, they must contain 80 percent fat.
A spread that is neither butter nor margarine is usually a plant-based choice, has no cholesterol and is lower in fats.
But spreads also contain more ingredients, such soy or flavorings. They contain a combination of oils, with palm oil making a frequent appearance. People with food allergies or sensitivities should note that these substitutes might contain milk and/or soy, both common allergens.
When It Comes to Baking
The video "Butter vs I Can't Believe It's Not Butter in Betty Crocker's Gluten Free Cookie Mix" demonstrates the difference between butter and spread. The butter cookies had a better crumb than the spread, and tasted richer.
But the competitor did well, making a good cookie without milk fats. A lower fat spread though, with less vegetable oil content may not perform well with this, or any, gluten free baking mix. The fat content was very close in both products, but we see by the results that it isn't just how much fat is called for, but the kind of fat we use.
Butter, though, contains cholesterol, and for this cook, that can be a problem. Testing the alternative spread in this mix I see there is a difference in the results. But as you can see in the pull-out, each cookie has 10 mg of cholesterol from the butter. The spread cookies may not be as rich and may crumble a bit, but I Can't Believe It's Not Butter makes a pretty good cookie.