Can anyone explain the difference between (regular) Oatmeal and Quick Oatmeal especially as far as cooking/baking are concerned?

Here is tghe clearest explanation I found 

Rolled oats have the bran mostly removed and are rolled flat to make them easier to cook. With the bran removed, they have less fiber than steel-cut oats.

Quick-cooking and instant oats are rolled oats that have been cut into smaller pieces and rolled thinner, thus cook quickly. They are an easy source for preparing many oatmeal dishes.

http://cancerdietitian.com/2008/11/quick-oats-steel-cut-oats-or-regular-oats-whats-the-difference.html

I find they both work fine for baking and I just use which ever ones I have in the house at the time. 

As quick oats are thinner, they will have less fiber.  But they seem to work the same as rolled oats in cookies.  Steel cut is in chucks rather than flat.  More fiber.  I would not recommend them for cookies.  Probably fine for muffins or breads.

Thanks.  Both of you answered all my ?s.  So I can bake cookies and use either Rolled or Quick and my cookies will be OK!