Ok,
ovulation usually happens around the 14th day of a normal 28 day menstural cycle. Before ovulation what happens is a hormone is produced which is a follicle stimulating horomnoe (fsh) which promotes growth of the follicle (egg sac) and helps to stimulate the ovaries to produce estrogen which builds up the lining of the uterus. At day 14(ovulation day) a mature ovum (egg) bursts out of the follicle into the ovduct (fallopian tubes) (conception usually takes place in the upper 1/3rd of the ovduct) if a little sperm does not get to it , it is flushed out of the body when your period comes.

In easier terms ovulation is when an egg is released!

But then again I have read studies where they believe ovulation happens many times throughout the menstural cycle.