Malignancy of the ovary cannot be diagnosed with any certainty by ultrasound. The best that can be done is to identify characteristics that make it more likely to be malignant or benign.
Multiloculated cysts (septations within a cystic area), solid areas, bilateral lesions (cysts on both ovaries) and other characteristics, seen by the ultrasonographer means that there are an increased chance of malignancy.
There is also, an increased chance of an ovarian tumor being malignant at older ages, so is the chance after menopause.
Septation just means a thin boundary between two collections of fluid and these ovarian cysts are known as complex ones.
When you are going to see your gyno?