Both are very similar. where as a popover is usually baked in a butter lined pan, Yorkshire pudding uses the drippings from the roast. Yorkshires can be baked in a flat pan with or without the roast or as I've had to do many times in individual cups like popovers. If you are going to do individual "yorkies" skim the dripping from the roast pan and divide them among the popover cups. about 1/4"-3/8" in each cup is about enough. yes I did say inch. also Yorkshires have a tendency to deflate do to the fact that they are a little softer and more souffle like.
Any other culinary questions???