An area of abnormal cells that forms on the surface of certain organs, such as the cervix, vagina, vulva, anus, and esophagus. HSILs look somewhat to very abnormal when looked at under a microscope. They are usually caused by chronic infection with certain types of human papillomavirus (HPV) and are found when a Pap test or biopsy are done. If not treated, these abnormal cells may become cancer and spread to nearby normal tissue. A HSIL is sometimes called moderate or severe dysplasia. Also called high-grade squamous intraepithelial lesion.