Ovarian vs Primary Peritoneal

I was diagnosed with ovarian stage IIIc in May, 2004. The team opted to give me three rounds of carbo/taxol, then hyst and debulk.  After surgery the gyne/onc surgeon was very pleased with what he saw intraoperatively and said I was now, "probably" Primary Peritoneal, and grade III.  I have asked and got a few answers.  I'm a little confused so if anyone could further explain what changes it to primary peritoneal and what else this means for me, I would appreciate it.  I have responded very well to chemo dropping my Ca 125 to 13 and after three rounds post-op, CA 125 = 9. I will have another 3 for a total of 9, (3 pre-op/6 post-op). Thanks in advance.