What Does Follicles Size Of 21mm During PCODsuggest?

i have pcod problem,my doctor asked me to use letroz tablets from day 3 of my menstrual cycle,and asked me to come for follicular study on day 8th,and in the report follicules were of 21mm in day 8th,what does it mean,am i having cyst,i badly want to conceive.