NN is an acronym used primarily on IRC and other cheat medium. Means "night, night". Closely related to np, nm, etc.
Note: This is merely a placeholder node. If you'd like to write up something a little more complete /msg me when you're done and I'll take this node down. Another note: Seriously, why all the downvotes? Isn't the point of E2 that there should be information on EVERYTHING? What more could one write on the acronym 'NN'? Do you wish it were never noded at all? Am I the only one that turns first to Google and E2 when searching for silly things everyone says but I don't know? What is with you people? Have you no heart? If I prick you, will you not bleed?
This (crappy, crappy) writeup (I was so young, please forgive me) is released under the GFDL, version 1.2 or any later version.