1) Cyst 
<obstetrics> A clogged milk duct, often associated with childbirth. ... (09 Oct 1997) ... 
(gә-lak´to-sēl) a milk-containing, cystic enlargement of the mammary gland; called also lactocele.
Type: Term Pronunciation: gă-lak′tō-sēl Definitions: 1. Retention cyst caused by occlusion of a lactiferous duct. Synonyms: lactocele
A cyst that forms in one or more milk ducts in the breast due to a clogged duct during lactation or breastfeeding. The cyst is usually small and filled with milk. Common symptoms of the cyst include breast pain and a lump within the breast. Treatment involves aspirating the cyst. Synonym(s): Milk Retention Cyst Lacteal Cyst
[n] - a cystic tumor containing milk or a milky substance (especially in the mammary glands)
a milk-filled tumour in a blocked breast milk duct