How is shortening different than butter or margarine, regarding nutrition and healthiness? why the name "shortening"? does it make cooking time short?

Chemistry: Fats make pastries less stretchy ("shortening") and more crumbly; by convention, "shortening" is cooking fat solid at room temperature that isn't margarine or butter. Some are artificially hydrogenated producing trans-fats, supposedly unhealthy -- a claim based on people's recollections, with contradictory results, and no good animal model. I'm reserving judgement, though they're mostly gone.

Yes: Shortening can be from animal lard or vegetable fats. Refers to fat that is solid at room temperature. It is called shortening since it prevents cross-linkage between gluten molecules, thereby preventing elasticity. That's why it makes a flaky crust pie or crumbly cookies. It does not make cooking time shorter. It also has a higher smoke point than butter or margarine; good for deep frying.