When a woman reaches 40-50 years old, her menstrual cycle usualy becomes irregular, what stage is this called?

When a woman reaches 40-50 years old, her menstrual cycle usualy becomes irregular, what stage is this called?-and what other symptons may she have?

 Simple irregularity has no particular name, though depending on the details it may be pathological and require investigation. The menopause, which in the UK now occurs at 51, has a normal range of 45 to 55. It results in less frequent and lighter periods as it approaches. 

 It's called "perimenopause". Other symptoms may be hot flashes, night sweats, reduced sex drive, headaches, unexplained weight gain and bloating. Everyone is different.

It can last for a few years, even as many as 10 before menopause (which means NO periods). Menopause is when you do not have any periods or bleeding for a year.