Bonus shares are additional shares given to existing shareholders without cost based on the number already owned, representing a company's accumulated earnings not paid as dividends. These earnings come from sources like retained profits, reserves, securities premium, and realized capital profits. Issuing bonus shares requires specific prior permission from the RBI. The advantages are increased share marketability and holdings, plus retained profits can fund development. Disadvantages include a decline in EPS and future dividend rates, and potential share speculation.