1.Someone who resides, or has been brought up in the city of Delhi.
2. Can also be used for people living in the NCR region (Gurgaon/Noida) provided, again, they have lived a few years in Delhi, and moved out (due to NCR's proximity to office, cheaper housing et al)
Anurag: Hey, I just passed out from school, and I'm shifting to this place in Gurgaon. Damn, am I still a Delhiite?
Delhiite living in Delhi: Yeah dude, chill, you're cool :)