Amenorrhea is the absence of menstrual periods in a woman of reproductive age.
It is classified into two types:
1. **Primary Amenorrhea**: This occurs when a female has not begun menstruating by the age of 15, despite normal growth and secondary sexual characteristics, or by age 13 without the development of secondary sexual characteristics.
2. **Secondary Amenorrhea**: This occurs when a woman who has previously had normal menstrual cycles stops menstruating for three months or more.
Causes of amenorrhea can include hormonal imbalances, genetic conditions, structural problems in the reproductive organs, excessive exercise, stress, eating disorders, and certain medical conditions or medications. Diagnosis and treatment depend on the underlying cause.