Anovulation - absence of ovulation; this can be caused by breastfeeding and is referred to as Lactation Amenorrhea.

Alveoli - glandular tissue that produces and secretes breast milk. These grape like clusters in the breast are grouped into bunches to form lobules.

Areola - the circular, dark-colored skin that surrounds the nipple.

Bilirubin - a by-product of the extra red blood cells a baby needs while in the womb. An excess of bilirubin is known as jaundice, and can cause skin and eyes to take on a yellowish tone.

Breast shell - a plastic shell that fits over the nipple, used to correct flat or inverted nipples.

Breast shield - a thin silicone shield that is placed over the nipple and areola during nursing.

Colostrum - thick, dark or yellowish fluid secreted from the breast during the first few days following the birth of a child. Colostrum is very rich in nutrients and will help protect your baby against disease. Colostrum is also sometimes secreted during pregnancy.

Coopers ligaments - ligaments in the breast that support the breast tissue.

Engorgement - occurring when breast milk builds up in the breasts, this condition can cause breasts to feel swollen, hard, and painful. Engorgement can also cause blockage in the milk ducts.

Flat nipple - a nipple that does not protrude (extend outward) from the body or become erect when stimulated or cold.

Glandular tissue - found throughout the body, glandular tissue is involved in the production of milk in the breasts.

Inflammation - occurs when an area on the body is irritated or infected, causing localized swelling, heat, discoloration and pain.

Inverted nipple - a nipple that retracts into the body, rather than protrudes when the areola (the dark area surrounding the nipple) is compressed.

Jaundice - caused by an excess of bilirubin, jaundice causes yellowing of the whites of the eyes and skin. Jaundice is relatively common among newborns, and is treatable.

Lactation - the secretion of breast milk, or breastfeeding.

Lactation amenorrhea - absence of ovulation caused by breastfeeding.

Lactose - a sugar found in breast milk, as well as in dairy products like cheese and butter.

Let-down - Reflex that causes milk to be created and flow through the milk ducts and from the breast.

Milk ducts - ducts in the breast that carry milk from the alveoli to the nipple.

Mastitis - generally occurring in breastfeeding women, mastitis causes the breasts to feel hard, sore or uncomfortable. Mastitis is caused when bacteria enters the breast through a break or crack in the nipple’s skin (such as those caused by chapped nipples) or by a plugged milk duct.

Milk-ejection reflexsee let-down reflex.

Montgomery glands - also known as areolar glands, these are small glands underneath the areola which can enlarge during pregnancy and breastfeeding and look somewhat like pimples on the areola. Montgomery glands secrete oils that lubricate the nipple.

Nipple - the protruding part of the breast that extends and becomes firmer upon stimulation or in cold temperatures. In breastfeeding, milk travels from the alveoli to the nipple.

Nipple shield - a latex or silicone nipple used during nursing to ease breastfeeding and protect the mother’s breast against irritation.

Oxytocin - a hormone that helps produce the milk-ejection reflex. Oxytocin also causes uterine contractions, which can help a mother’s uterus return to its normal size after giving birth.

Phototherapy - light treatment in which the baby's skin is exposed to special fluorescent lights to treat jaundice. In mild cases, exposure to sunlight is sometimes recommended.

Plugged (milk) duct - often caused by mastitis, plugged ducts occur when small milk ducts in the breast become blocked.

Primary lactase deficiency - also known as lactose intolerance, lactase deficiency causes an inability to digest lactose, a sugar found in milk and milk products, resulting from the lack of the enzyme lactase. A lactase deficiency can cause discomfort, bloating, gas and diarrhea when consuming milk and dairy products.

Progesterone - a hormone produced by the ovaries. Progesterone, along with estrogen, prepares the uterus (womb) for ovulation each month, and supports the fertilized egg if pregnancy occurs. Progesterone also assists in milk production and breastfeeding.

Progestin - a hormone that assist with various functions in the uterus. When combined with estrogen, progestin prevents thickening of the lining of the uterus. Progestins are also prescribed to regulate and treat irregularities in menstruation, encourage or maintain a pregnancy, or treat irregular or heavy uterine bleeding.

Prolactin - a hormone that stimulates the breast to produce milk for breastfeeding. Prolactin also inhibits ovulation.

Rooting - a reflex exhibited by newborn babies, along with the reflexes for sucking and swallowing. Rooting involved the instinctive turning of the head to search for the nipple and milk.

Thrush - a common yeast infection of the mouth and throat caused by the fungus Candida albicans, marked by white patches in the mouth. Thrush can also occur in the gastrointestinal tract and vagina, and can cause certain types of diaper rash in infants.

For more useful health terms, go to the National Women’s Health Information Center’s Glossary of Health Terms.