Breast pump syringe and valve, illustration. Valve (top) being fitted to the syringe part of a breast pump. A breast pump is a device used to extract milk from the breast of a woman after she has given birth. The production of breast milk following pregnancy is known as lactation. A breast pump is used by those with young children to relieve overfull breasts during early lactation and to express milk for future use if there are problems with normal breastfeeding. Breast milk is considered an ideal mix of nutrients and antibodies to feed and protect a baby.