Wikipedia
Micromastia (also called hypomastia, breast aplasia, or breast hypoplasia) is a medical term describing the postpubertal underdevelopment of a woman's breast tissue. Just as it is impossible to define 'normal' breast size, there is no objective definition of micromastia. Breast development is commonly asymmetric and one or both breasts may be small. This condition may be a congenital defect associated with underlying abnormalities of the pectoral muscle (as in Poland's syndrome), related to trauma (typically surgery or radiotherapy) or it may be a more subjective aesthetic description.
Self perceived micromastia involves a discrepancy between a person's body image, and her internalized images of appropriate or desirable breast size and shape. Societal ideals over breast size vary over time, but there exist many conceived ideas involving breasts and sexual attractiveness and identity across different cultures.
Micromastia is a genus of fungi in the Ascomycota phylum. The two known members are Micromastia fimicola. and Micromastia trigonospora. The relationship of this taxon to other taxa within the class is unknown ( incertae sedis), and it has not yet been placed with certainty into any class, order, or family.