Menstrual disorders, also known as menstrual irregularities or abnormal uterine bleeding, refer to a range of conditions that involve variations in the normal menstrual cycle. The menstrual cycle is the monthly hormonal process that occurs in the female reproductive system, leading to the shedding of the uterine lining (menstruation) in the absence of pregnancy. Menstrual disorders can encompass several different patterns of irregular bleeding, including:

1. **Amenorrhea**: This refers to the absence of menstrual periods. There are two types of amenorrhea:
   - Primary amenorrhea: When a girl has not started her period by the age of 16.
   - Secondary amenorrhea: When a woman who previously had regular periods stops menstruating for at least three months.

2. **Dysmenorrhea**: This is severe menstrual pain or cramps that are often accompanied by headaches, nausea, and other symptoms.

3. **Menorrhagia**: Excessive or prolonged menstrual bleeding that lasts longer than 7 days or involves unusually heavy flow.

4. **Metrorrhagia**: Irregular bleeding or spotting between menstrual periods.

5. **Polymenorrhea**: Menstrual cycles that occur more frequently than the normal 21 to 35-day range.

6. **Oligomenorrhea**: Infrequent or irregular menstrual periods occurring at intervals greater than 35 days.

7. **Anovulation**: A lack of ovulation (release of an egg from the ovary) in a menstrual cycle, which can lead to irregular or absent periods.

8. **Premenstrual Syndrome (PMS)**: A collection of physical and emotional symptoms that occur in the days leading up to menstruation, including mood swings, bloating, breast tenderness, and fatigue.

9. **Premenstrual Dysphoric Disorder (PMDD)**: A more severe form of PMS characterized by intense emotional and physical symptoms that significantly affect a woman's quality of life.

Menstrual disorders can have various causes, including hormonal imbalances, medical conditions (such as polycystic ovary syndrome or thyroid disorders), stress, changes in weight, medications, and sometimes underlying reproductive health issues. It's important for individuals experiencing menstrual irregularities to consult a healthcare provider for proper diagnosis and treatment. Depending on the underlying cause and severity of the disorder, treatment may involve lifestyle changes, hormonal therapies, medications, or in some cases, surgical interventions.