A door closer is a device used to close a door automatically after it has been opened. The term 'door closer' can refer to several different types of devices, including a MAT, which is a mechanical arm that attaches to the door and frame; a LATCH, which is a type of lock that holds the door closed; a HASP, which is a metal loop that is secured with a padlock; and a NAIL, which is a metal fastener that is driven into the door frame.