265 is the width is mm and the 75 is the aspect ratio, that is the height to the width. Your tire is 75% as tall as it is wide (the section, not the entire tire).
P = Passenger car tire (LT would mean Light Truck)
215 = width of tire in millimeters
65 = aspect ratio, or ratio of tire width to tire height
R = construction, Radial
15 = rim diameter code
i see that i was a little late, but i hope this helps....