The act of working on, or relating to, one's Ph.D.
Primarily used by postgraduate students in an attempt to refer to the overwhelming amount of work they have to do in a lighthearted, and positive manner -- despite the realistic stress, pressure, and guilt that are ever-present during doctoral study.
"I can't go out tonight, I have PhDness to catch up on."
Q: "Hey, what have you been up to lately?"
A: "Just PhDness."