Trepanning, also known as trepanation, trephination, trephining or making a burr hole (the verb trepan derives via Old French via Medieval Latin from the Greek noun of relevant meaning trypanon, literally "borer, auger") is a surgical intervention in which a hole is drilled or scraped into the human skull, exposing the dura mater to treat health problems related to intracranial diseases. It may also refer to any "burr" hole created through other body surfaces, including nail beds. It is often used to relieve pressure beneath a surface. A trephine is an instrument used for cutting out a round piece of skull bone.