Hasp and staple locks feature a hinged plate with a long, thin opening (the hasp) and a separate plate with a loop (the staple). They're most often used for extra security on gates or shed doors.
The hasp is fitted to the edge of a door or gate, while the staple is fitted to the door frame or gate post. When the hasp is moved to cover the staple, the loop of the staple fits through the hole of the hasp. Then a padlock can be threaded through the loop of the staple so that the hasp cannot be moved back and the door cannot be opened.