Hi all, (Thank you for the continuing responses to my other questions...) I am gaining more and more understanding of differential forms and differential geometry. But now I must ask... Why the words? I understand the exterior derivative, but why is it called "exterior?" Ditto for CLOSED and EXACT forms: I understand the definition, but nothing in that definition informs me of why that word was chosen. Could anyone elaborate, simply, on the reason for the words: exterior, closed, exact?