Living Glossary
Welcome to the Living Glossary, a growing collection of reproductive health terms explained in plain language.
As new topics are explored through Menstruation to Menopause, new terms will be added to the glossary. Existing definitions will be reviewed periodically to help ensure they continue to reflect current medical guidance.
The Living Glossary draws from trusted medical resources, including the American College of Obstetricians and Gynecologists (ACOG), the Office on Women's Health (OWH), and MedlinePlus.
Browse the glossary by selecting a letter below.
Browse by Letter
H
Hormones
Chemical messengers made by glands and other tissues in the body that help control many body functions. Reproductive hormones, including estrogen and progesterone, help regulate the menstrual cycle and play an important role in the changes that occur throughout our reproductive lives.
M
The point when menstrual periods have permanently stopped and pregnancy is no longer possible naturally. Menopause is reached after 12 consecutive months without a menstrual period, when there is no other medical reason for the periods to have stopped. Menopause most commonly occurs between ages 45 and 55.
Menopause
Menstruation
The process when the uterus sheds its lining if pregnancy does not occur. The blood and tissue from the uterine lining leave the body through the vagina. Menstruation is also commonly called a period.
P
Perimenopause
The transition leading to menopause when hormone levels begin to fluctuate, causing changes in the menstrual cycle. These changes may include cycles that are longer or shorter than usual, heavier or lighter bleeding, or skipped periods. Other symptoms may include hot flashes and trouble sleeping. There is no specific age when perimenopause begins; it may start as early as the 30s or as late as the 50s. Perimenopause ends after 12 consecutive months without a menstrual period, when menopause is reached.