Source : Webster's Revised Unabridged Dictionary (1913)

Ovulation \O`vu*la"tion\, n. (Phisiol.)
   The formation of ova or eggs in the ovary, and the discharge
   of the same. In the mammalian female the discharge occurs
   during menstruation.

Source : WordNet®

ovulation
     n : the expulsion of an ovum from the ovary (usually midway in
         the menstrual cycle) [ant: {anovulation}]