ghost gun

Meanings

1. A gun without serial numbers that cannot be easily tracked, especially a homemade gun built with nonregistered, partially finished, or 3D printed components.
2. A gun that is not detectable by standard gun detection measures, such as a gun without much metal and thus unable to set off metal detectors.

Etymology

From ghost + gun. Derived from the fact that these firearms are unserialized, difficult to trace, and often remain invisible to the tracking and regulation covering traditionally manufactured firearms. First use appears c. 2001 in Sunday People.