Menstruation, or menses, is when an unfertilized female has blood come out of her vagina for 2–7 days every month. A more common word for menstruation is a "period".

Summary 
Inside the thick part of the uterus are blood vessels and nutrients that a baby will need to grow. Every month in a human female who has gone through puberty, the brain sends signals to the ovaries that tell them to release an ovum (or egg). The ovum then travels through the fallopian tubes (with the expectation of becoming fertilized by a sperm cell) into the uterus. If an ovum is fertilized, it sticks to the wall of the uterus and starts to grow. If the ovum is not fertilized, it does not stick. The uterus then gets rid of the ovum and the extra tissue by releasing it from the body. The tissue and blood flows out of the uterus through the vagina. This is called menstruation or having a period. The bleeding normally lasts about 3-5 days, though some people may bleed longer or have a bit of bleeding between periods.

The uterus then starts preparing for another ovum. For most people, the time between their periods is about one month. For about 2 years after menstruation starts, the time between periods is not always the same. Some menstruators may skip a month, or have 2 periods close to each other. It is also possible and normal (within reasonable limits) to have cramps (rather painful squeezing feelings) or to feel bloated (swollen up) in the abdomen at periods.

People who have periods often use sanitary napkins or tampons to soak up the blood and tissue. A sanitary napkin is a piece of material that absorbs (takes in) liquids which is worn between the vulva and underpants. A tampon is a stick of absorbent material that is placed in the vagina. Pads and tampons can be disposable or reusable.The use of a menstrual cup or disc is also possible. A menstrual cup is a silicone cup that is inserted inside the vagina to collect blood and other tissues. A menstrual disc follows the same concept but is made of more flexible material and is round and flatter than a cup, it is also inserted higher in the vagina.

Cycle

Menstruation
Most people menstruate for 3–5 days every month. However, anywhere from 2–7 days is normal. The amount of blood lost is normally about 50ml. Menstruators usually use a pad or a tampon to keep the blood from staining their undergarments, but there are many other forms of sanitary protection.

Menopause
Menopause is menstruation stopping at the age of around 45-70, which is caused by hormones. Symptoms include irritability, heat, vaginal burning and/or discomfort, and vaginal dryness. A slang word for it is called "the change". Most people must take a few months to adjust to the dryness. After they stop their period they can no longer produce babies.

Physical appearance 

The fluid that comes out looks like blood, but it is more than just blood. It also has endometrial tissue. This is the tissue that lines the inside of the uterus (womb).

Menses happens in the first days of the menstrual cycle. This is the changes that happen in a woman's body every month. These changes are started by changes in hormone levels in the blood. These changes also cause a person to ovulate and make an ovum (also called "egg"). Menstruation usually starts around the age of 11, even as early as 9 years old, and ends when the menstruator is too old to have children. However, some females can still have children from the age of 50-70.

Effect 

Some people have pain in the low part of the abdomen when they menstruate. This is called dysmenorrhea, or cramps. Extreme and continuous cramps are not normal and should be checked upon with a medical practitionner. The hormones that are produced before and during a period can also make a woman feel moody, or just strange. This is called premenstrual syndrome (PMS), or premenstrual tension (PMT). A person can feel bloated or swollen and have long cramps. Some menstruators have extremely bad reactions to menstruation and may even feel suicidal. This is called premenstrual dysphoric disorder, or PMDD. Other physical effects include headaches, tender berasts, lower back pain, fatigue, acne, diarrrhea or constipation, trouble sleeping and more.

Materials 
Most menstruators use something to absorb or catch their menses. There are a number of different methods available. The most common methods of absorbing the flow are sanitary towels (sometimes called "pads"), tampons and padded underwear. Some people use sea sponges, towels and other reusable absorbing items.

In addition to products to contain the menstrual flow, pharmaceutical companies likewise provide products — commonly non-steroidal anti-inflammatory drugs (NSAIDs) — to relieve menstrual cramps. Some herbs, such as dong quai, raspberry leaf and crampbark, are also claimed to relieve menstrual pain, however there is no documented scientific evidence.

Notes
3. https://www.yourperiod.ca/normal-periods/symptoms-of-menstruation/ 
Female reproductive system