A hole or opening in an object that shouldn't exist. In particular, one that is a result of poor engineering and/or manufacturing. Stoneciphers can and often do lead to catastrophes. Named for Harry Stonecipher, CEO of Boeing from 2003 to 2005, who said "When people say I changed the culture of Boeing, that was by intent, so that it's run like a business rather than a great engineering firm.
The 737 door plug blew out leaving a gapping stonecipher.