Ovulation is the period in a female's menstrual cycle by which a mature ovarian follicle ruptures and discharges an ovum (also known as an oocyte, female gamete or casually an egg). The time immediately surrounding ovulation is referred to as the ovulatory phase or the periovulatory phase. (from Wikipedia)
Around the middle of your cycle, a ripe egg or ovum is released from one of your ovaries. This is called ovulation. The human female body has two ovaries, each the size of an almond. These ovaries produce the eggs.
The egg is released into the Fallopian tube (a tube that connects the ovary and the uterus. This is the place where fertilisation takes place between egg and the sperm, if you make love around the time of ovulation) and is stroked down its length by the 'fingers' which help to direct the egg down into the tube.
At the same time, the lining of your womb (or uterus is where your baby grows) begins to thicken and the mucus in the cervix becomes thinner so that sperm (if you had intercourse) can swim through it more easily.
Ovulation is characterised by an increase in the levels of a hormone called Luteinising Hormone produced by the brain and responsible for the release of eggs from the ovary every month (hormonal surge ) and a small increase in temperature.
Once released, your egg can survive upto 24 hours.