What is the difference between sleet and freezing rain?

Sleet bounces, freezing rain does not :)

Really, that's the difference.

Freezing rain is snow that melts into water and does not re-freeze before hitting the ground.

More specifically, freezing rain freezes on contact with a cold surface. See Freezing Rain: supercooled droplets freezing on impact this tends to put a coating of ice on whatever it sticks to. In a large amounts it can cause lots of damage due to it's weight pulling down power lines and trees.

Sleet is in the form of small ice pellets