"Doxing" is a neologism. It originates from a spelling alteration of the
abbreviation "docs", for "documents", and refers to "compiling and releasing a
dossier of personal information on someone". Essentially, doxing is revealing
and publicizing the records of an individual, which were previously private or
difficult to obtain.
The term dox derives from the slang "dropping dox", which, according to a
contributor to Wired, Mat Honan, was "an old-school revenge tactic that emerged
from hacker culture in 1990s".