Tumor is just one of several terms used to denote a "thing" growing in or on an ovary. My own cyst was referred to at various points prior to my surgery as a "cyst," "complex cyst," "mass," "tumor," and "solid complex mass."
Complex cyst means that there's something in it other than fluid. Could be septated, hemmoragiac (sp?), dermoid and I'm sure there are other types too. I'm sure someone will be along shortly with additional info too!