Sorry, but this is such a lovely entry from the Urban Dictionary:
nang
something that's cool
The word originated in Hackney, London. Specifically Kingsland Secondary School (now sadly gone).
The word is a direct product of one Nang Phan, an ex-student of KS. It came about through boys in years above her chiding "ahh, Nang you're nang". It caught on like wildfire from there.
by Nang's Best Friend August 11, 2003