Gynecomastia or Gynaecomastia, pronounced /ˌɡaɪnɨkɵˈmæstiə/, is the abnormal development of large mammary glands in males resulting in breast enlargement. The term comes from the Greek γυνή gyné (stem gynaik-) meaning “woman” and μαστός mastós meaning “breast”. The condition can occur physiologically in neonates (due to female hormones from the mother), in adolescence, and in the elderly (Both in adolescence and elderly it is an abnormal condition associated with disease or metabolic disorders). In adolescent boys the condition is often a source of distress, but for the large majority of boys whose pubescent gynecomastia is not due to obesity, the breast development shrinks or disappears within a couple of years. Gynecomastia should be distinguished from muscle hypertrophy of the pectoralis muscles caused by exercise e.g., swimming, bench press, etc. (source: Wikipedia)

Some Health conditions that can cause gynecomastia

• Hypogonadism – Interference with normal testosterone production, such as Klinefelter syndrome or pituitary insufficiency, can be associated with gynecomastia.
• Aging – Hormone adjustments that happen with aging can cause gynecomastia. This is even more prevalent with men who are overweight
• Tumors – Some tumors can produce hormones that alter the male-female hormone balance.
• Hyperthyroidism – In this condition, the thyroid gland produces too much of the hormone thyroxine.
• Malnutrition and starvation – Inadequate nutrition due to starvation or other, can cause a hormonal imbalance. This happens when testosterone levels drop, but estrogen levels remain constant.
• Kidney failure – Nearly 50% of patients being treated with regular hemodialysis experience gynecomastia due to hormonal changes.
• Liver failure and cirrhosis -  Hormonal fluctuations related to liver problems as well as medications taken for cirrhosis are associated with gynecomastia.