Was planning to see classmates at upcoming 20th reunion. Now I am hearing my best friend has ovarian insufficiency. What is that?

Premature menopause. Ovarian insufficiency is another way of saying someone is going through menopause. There can be various causes of why someone might go through this prematurely. This can be treated with supplemental hormones and should not keep your friend from attending the reunion.
Non-functioning ovar. Ovarian insufficiency is a new term for what we used to call premature ovarian failure or premature menopause. The ovaries stop responding to FSH stimulation before the age of 40. This means no ovulation, low estrogen and menopausal symptoms. The ovaries will sometimes turn back on again but nothing can be done to force an ovulation.