A little confused, please shed some light

I'm not sure I'm posting this in the right place. My story started in Sept. 2010 with a trip to the ER w/ burning pain in right groin area. My blood and urine were okay. They diagnosed as urinary track infection. My tummy was a little bit bloated and hard though and the ER doc asked why it was hard. I told him the only thing I could think of was that I did a lot of isometric exercises and he said it could be muscle.I went away thinking I was okay.
The months went on and my tummy slowly got a bit bigger. I thought this was due to aging(I'm 39), not exercising enough, poor posture, poor diet, and even a digestive issue as I've been constipated for a good portion of my life.
I felt fine and I didn't too much of it until Christmastime this last year. I noticed I was getting more heartburn and indigestion. I then stopped drinking wine and tried to eat even better than I had been eating. My indigestion seemed to improve and went on with my daily life.
It wasn't until about a month or so ago that I knew something definitely wasn't right. My abdomen grew a lot bigger and I started developing pain. I went to doc's, he ordered a CT scan and I was diagnosed with a sizable abdominal mass that looked like it was benign due to it's shape and growth. I was given the best and worst(cancer) case scenarios by oncologist and what he would have to remove in each case. He said he thought the problem may be stemming from my one ovary.
My bloodwork was okay. I had surgery and they removed one of my ovaries and fall. tubes. They also precautionarily removed my appendix as a judgement call. They determined during the surgery that it was not cancer and on my discharge papers, "ovarian cyst" is listed as official cause.
Here's where I need the light.... Went to doc's today. He said the pathology is just a bit different than we originally thought. It's not cancer, but it was a tumor. It's something in between. The pathologists are vague about it. This means you will have to be monitored every 4-6 months. If you notice any changes or distention you must see us. He doesn't want me to wait as he thinks I had waited too long this time. He said every 4-6 mos. I will have a check-up, bloodwork, and CT scan if necessary, but there's a possibility it may never come back.
My questions are, "What does "in between" mean? And is this monitoring standard? What do I make of this?
I know there are so many suffering and I pray for them every day. My dad died of lung cancer(smoked 4ever), so I know how hard it is. I just feel frightened again and do not want to spend the next 4 mos. living in fear.
Thank you for your time.