Hi, I understand that from my EM class there exist a surface integral which is actually a way of summing infinitesimally small surface elements ds. But then I ran into some theorems on internet and I saw the denotation of double integral, over a surface S. And they called that a surface integral. But I learnt a surface integral to be a single integral. Can somebody clear this misunderstanding for me? Mainly this came from Stokes' theorem. Theorem it self isn't a problem, just the denotation of surface integral as double integral is.