When a female is having her 'period'. The time of menstruation for a woman, when the body discharges blood, and tissue from the vagina. Occurs in non pregnant women.
Other terms used for this include, on the saddle, on the plug, that time of month, wet season, mother nature's gift, the vapours, out of order, off duty.
Usually is a sign of puberty in a female, and is for those who are not pregnant.
The discharge of blood, that occurs regularly, during a normal body cycle.
Not all women, who are at that time of month, experience mood swings either, which is another issue, that is associated with menstruation.