Derived from suffix -ness. It is the distinct aspect(s) exhibited by someone/something that makes he/she/it unique.
Person 1: "That tree has a certain kind of nessiness about it. I can't tell exactly what it is though."
Person 2: "I think it's the neon pink leaves."
Person 1: zomg i pwn!! im so 1337!!! itz part of my nessiness!!!!!!!
Person 2: So are your obsessions for lolcats.com and ebaumsworld.com.
Person 1: can i has cheeseburger?