High risk pregnancy

I'm confused on what high risk pregnancy is. I think I might be high risk. My doctor makes me get ultrasounds monthly and soon to be bi-weekly. I also see my OB once or twice a month. I have heart  irregularities and they constantly are checking my heart. They told me I may not vaginally deliver and I might need a planned C-section. They haven't said in their own words "high risk" they say "close monitoring". I just want to know what high risk means.