PCOS is Polycystic Ovarian Syndrome. There's a pretty good webpage here
http://www.soulcysters.com/, and
http://centerforpcos.bsd.uchicago.edu/ is also good.
This paragraph is taken from the latter website:
Polycystic ovary syndrome is an endocrine (hormonal) disorder. Most often, symptoms first appear in adolescence, around the start of menstruation. However, some women do not develop symptoms until their early to mid-20's. Although PCOS presents early in life, it persists through and beyond the reproductive years.
PCOS is estimated to affect between 5% and 10% of women of reproductive age, thus making it the most common hormonal disorder among women in this age group. It affects women of all races and nationalities.
No two women have exactly the same symptoms. The following characteristics are very often associated with PCOS, but not all are seen in every woman:
Hirsutism (excessive hair growth on the face, chest, abdomen, etc.)
Hair loss (androgenic alopecia, in a classic "male baldness" pattern)
Acne
Polycystic ovaries
Obesity
Infertility or reduced fertility
In addition, women with PCOS appear to be at increased risk of developing the following health problems during their lives:
Insulin resistance
Diabetes
Lipid abnormalities
Cardiovascular disease
Endometrial carcinoma (cancer)
Because there is such variability in how PCOS presents itself, there is not universal agreement among health professionals on how to best define PCOS. What is clear, however, is that women with the disorder do not ovulate in a predictable manner and that women with PCOS also produce excessive quantities of androgens (particularly testosterone).
It is important to note that polycystic ovaries are not present in all women diagnosed with PCOS. Also, many women with regular menstrual periods and normal testosterone levels have cystic ovaries.
If women with PCOS don't always have polycystic ovaries, why is it called "polycystic ovary syndrome"?
It is important to make the distinction between polycystic ovaries and polycystic ovary syndrome. Polycystic ovaries are often, but not always, seen in women with PCOS. But, approximately 20% of women without menstrual or hormonal abnormalities have polycystic ovaries. The syndrome is thus defined by the menstrual and hormonal abnormalities with or without polycystic ovaries.
PCOS is also sometimes called "functional ovarian hyperandrogenism" or "ovarian androgen excess." But, because the term "polycystic ovary syndrome" has been used for more than six decades, and is well-entrenched in both common usage and medical literature, its use is likely to continue.
What causes PCOS?
PCOS develops when the ovaries overproduce androgens (eg, testosterone). Androgen overproduction often results from overproduction of LH (luteinizing hormone), which is produced by the pituitary gland.
Research also suggests that when insulin levels in the blood are high enough, the ovary can be stimulated to produce more testosterone. That is, the combination of having ovaries which are responsive to insulin and high insulin levels in the blood, can result in the overproduction of testosterone.
Obesity, which itself can cause insulin levels to rise, may intensify PCOS. Yet, not all women who are overweight develop PCOS. Thus, there appears to be something unique about PCOS both in the excessively high insulin production and the increased sensitivity of the ovaries to the insulin that is produced.
Hope this helps
Tess
What is PCOS?
I was told that it means Polycystic Ovarian Syndrom but then my sources are not that great so maybe someone else knows what it realy means 
