Menstruation

Discharge of bloody fluid from the uterus roughly once a month. Menstruation normally starts between the age of 11 and 15, and ceases permanently sometime after the age of 45. Menstruation occurs roughly every 28 days, and each menstrual period lasts for three to five days. Irregularities in the cycle and in the volume, color, and consistency of the flow, are referred to by the general name of menstrual irregularities.

Etymology

Chin 月 yuè, month; 经 jīng, warp, channel, rule.