OB/GYN: A commonly used abbreviation. OB is short for obstetrics or for an obstetrician, a physician who delivers babies. GYN is short for gynecology or for a gynecologist, a physician who specializes in treating diseases of the female reproductive organs. The word "gynecology" comes from the Greek gyno, gynaikos meaning woman + logia meaning study, so gynecology literally is the study of women. These days gynecology is focused largely on disorders of the female reproductive organs. An obstetrician/gynecologist (OB/GYN) is therefore a physician who both delivers babies and treats diseases of the female reproductive organs.