A darknet can be defined as a restricted, closed access, private network that is typically used for private communication. As previously mentioned, a darknet is simply a private peer to peer file sharing network.
What makes darknets truly different than other peer to peer networks is that users only connect to other trusted users. Darknets rely on specialized software; some examples include: WASTE, Freenet, and the unreleased HP Darknet, Veiled.
The real issue with darknets is the ability to transfer illegal content. Such software makes it possible for a small group of users, a terrorist cell, or child pornographers to silently trade files and information while staying out of sight of the general public.
As darknet software becomes easier to use, more and more average users will be able to move information covertly and avoid prosecution for transfer of illegal content. The result will be that it will become more difficult for law enforcement and investigators to gather data they need for prosecution.