What is the difference between front and rear motorcycle tires?

There are two main differences between a front and rear motorcycle tire. The rear tire is flatter while the front tire is more triangular in shape. The triangle shape of the front tire helps the bike enter and exit turns while the flatter shape of the rear tire gives the bike more stability. The second difference is that the forces generated on the rear vs. the front tire are reversed. The rear tire is subjected to acceleration forces while the front tire is subjected to the majority of the braking forces therefore the inner lacing of the tires are set up reversed.

That said, you can run a rear tire on the front if you reverse it so the rotational arrow is backwards. Do not attempt to run a front tire on the rear. You will lose the stabilizing effects of the rear tire and the tire will also wear out much faster since it doesn't have as much tread to start with.