What is the period? Read this summary. You'll probably want to learn even more about this fascinating biological process: the Mayo Clinic has a full explanation of what menstruation is, what to expect, what's normal, and what's considered medically irregular. The U.K.'s National Health Service also provides a guide to the period, and what happens during ovulation. This resource will give you even more information about the intricate ovulation process.

You may also want to read up in more detail about the various hormones that control the menstrual cycle. See here and here for information about follicle stimulating hormone, luteinizing hormone, estrogen, and progesterone. Curious about the role of the pituitary in all of this? See here and here to find out more.

When it comes to the female reproductive system, there are a lot of words to grasp: here are some sources that will help you understand more about ovaries, their follicles, and the miniscule oocytes within. This resource will give you a good sense of how the ovarian follicle matures in response to the body's hormones. Meanwhile, here's a web page with a helpful diagram that explains in detail how fertilization actually happens.

Finally, here's a helpful, detailed guide for anyone curious about what to expect during a first period. And, if you're interested in the evolutionary basis of this biological process, take a look at this TED-Ed video, which explains why women get periods in the first place. The answer might not be what you expect!