Gynecomastia, the enlargement of male breast tissue, is classified into four stages based on the severity of the condition. In stage 1, there is a small amount of breast tissue that is concentrated around the areola. In stage 2, there is moderate breast enlargement that extends beyond the areola, but the edges are not well-defined. In stage 3, the breast enlargement is more significant and there is excess skin in addition to the breast tissue. In stage 4, the breast enlargement is severe and the areola has become feminized, resembling that of a female breast.