The 275 tire is larger than the 265. It is .4 inch wider, .5 inch more in diameter, and 1.5 inch more circumference. The 275 costs a little more.
Some drivers have reported the 275 as having stiffer ride and more traction. Others have not noticed any difference as they are very close.
Driving with the 275 your speedometer will be off by about 1 mph than actual.
The 265 being not as wide may be a better choice for driving on snow.
They both fit 17 and 18 inch rims.
The numbers 275 and 265 mean the width in mm.
They both are radial tires.
Side by side comparison video:
Tire size info graphics guide:
