Ghost Gun Definition

noun
A gun without serial numbers, thus cannot be easily tracked, such as a home made gun.
Wiktionary
A gun that is untraceable, such as a gun that does not leave easily determinable correlations between bullets, brass, barrels, and the guns.
Wiktionary
A gun that is not detectable by standard gun detection measures, such as a gun without much metal thus unable to set off metal detectors.
Wiktionary