As far as I remember from flight school, the point of safe return (PSR) is the farthest point where you could still return and arrive at your departure aerodrome with reserves intact. The term 'point of no return' (PNR) refers to the same concept but implies arriving with tanks dry. That way, the PNR defines the so called 'radius of action', a term of military origin and mostly used in helicopter SAR missions. Sometimes PSR and PNR are used interchangeably, which might have led to your confusion.
Edit:
The point of equal time (PET) is the point where the flight time to your destination would be the same as the time back to your departure aerodrome. It's got nothing to do with PNR/PSR.
Last edited by hvogt; 30th September 2013 at 19:58.