Cervical intraepithelial neoplasia (CIN) is a precancerous condition characterized by abnormal growth of cells on the surface of the cervix, often caused by persistent infection with high-risk human papillomavirus (HPV) types. It is classified into three grades, CIN 1, CIN 2, and CIN 3, based on the severity of the dysplasia, with CIN 3 being the most severe and carrying the highest risk of progression to cervical cancer if left untreated.