John Doe:
(plural: ‘John does‘; female: ‘Jane Doe‘)

a John Doe (a man whose name or other identity is not known)
(in law & court of law, mostly in the USA) a man whose name is not known or not yet identified, or an imaginary man;
a typical average man; any man,

a Jane Doe (a woman whose name or identity is not known)
In some criminal cases, the police as well as the court keep the real name of a wanted criminal from going public but use the name ‘John Doe’ for a man and ‘Jane Doe’ for a female for fear of the criminal or their associates meddling with the investigation.
The police are looking for a John Doe who is wanted in a video piracy case.
When Charles was asked where he had got that secret information, he said he had heard it from some John Doe… to make it look as if the informer were just a man in the street.
There are more and more John Does and Jane Does cropping up every day in cases of copyright infringement or privacy policy violations, especially in cyber crimes.

(here the dead woman & her name were not known to anybody, so they buried her with the name ‘Jane Doe’)
for a news article that shows us how we come across this expression in our daily browsing, please click here,
for an article that shows us how this expression and John Doe Orders are used in legal issues and in countries other than the US, please click here,
for an article (a pod cast), with an audio clip, about a John Doe being sentenced, please click here
and
for a news release in which we see how this expression, Jane Doe, a female unknown person, is found in our daily news, please click here.
