The word "menstruation" comes from menses, the Latin word for "month." If you've heard friends talk about "that time of the month," you can probably guess that women menstruate approximately every month.
A menstrual cycle is the time between the first day of one period and the first day of your next period. The amount of time it takes for this to happen is about a month (the average cycle lasts 28 days). One complete cycle is made up of several phases:

Phase 1 - Menstruation (Having your period)
Your body is getting rid of tissue it doesn't need.

Phase 2 - Pre-Ovulation Phase (Right after your period ends)
Your body is preparing an egg for pregnancy.

Phase 3 - Ovulation
A lot happens in this phase, but basically the egg is released from the ovary into the fallopian tubes, and your body is preparing the uterus to receive a fertilised egg (if there is one).

Phase 4 - The Premenstrual (Luteal) Phase
If a woman has not become pregnant, the uterus gets ready to release the unneeded tissue that was prepared for the egg.

Did you know - You are born with all the eggs you'll ever have! When you were a 20-week-old female foetus (still in your mother's uterus) you had approximately 7 million eggs. However, only between 400 and 500 will ripen into mature eggs during your life – crazy!