Trepans is a word that refers to the act of perforating the skull, usually as a form of medical treatment. There are a number of synonyms for this word, including trephine, cranial perforation, cranial opening, and skull surgery. These variations on the term generally refer to different aspects of the procedure, whether it be the tool used, the nature of the operation, or the intended outcome. While the practice of trepanning has been in use for thousands of years, it remains a relatively obscure and controversial procedure, with many modern medical professionals opting for less invasive and risky methods of treating brain injuries and disorders.