Wikipedia has a solid description of what "doxing" is:
Doxing is the Internet-based practice of researching and publishing personally identifiable information about an individual.
They also make a claim that the word is an abbreviation for "document tracing" but none of their sources confirm this. It seems like a completely unsubstantiated claim. Terms that appear in internet culture are notoriously hard to track but I'm finding it hard to believe that "dox" is short for "document tracing" considering the only relevant part of the longer phrase is "doc".
One of their linked sources even disagrees:
The term "dox" (also spelt "doxx", and short for "[dropping] documents").
Does anyone know how long this term has been used and where it originated? Is it really an abbreviation for "document tracing"?