In my experience:
VRS: a well defined and developed state where the rotor is operating in a self-sustaining vortex resulting in high rate of descent, requires positive action to exit
Settling with power: a state where the helicopter is continuing to descend despite power applied, usually made worse by recirculating air, turbulence, and high DA conditions
Overpitching: a condition where the pilot has commanded a higher pitch setting on the rotor blades than the engine(s) can sustain, causing a RRPM droop and subsequent loss of performance
all different and dangewrous in their own right.