Sleet
Sleet is defined as frozen raindrops that bounce on impact with the ground. Sleet is shown as pink in this picture on the cold side of the warm front. As temperatures continue to decrease, freezing rain turns into sleet. Sleet is less common than freezing rain, and the largest difference between the two is that sleet is frozen before it comes in contact with a cold surface.
As you can see in this picture, rain falls from the clouds and encounters a cold belt of air causing the raindrops to freeze into snowflakes. Then the frozen rain hits a belt of warm air, causing them to partially melt. Then the wet snow hits a final belt of really frigid air which causes them to refreeze into sleet.
Sleet develops under very specific weather conditions. It is difficult to forecast. It is similar to freezing rain with the respect that it makes slippery conditions, but another difference between the two is that sleet is easily visible and does not stick to objects while freezing rain is transparent and sticks to everything.
Sleet often falls with snow and rain. It occurs only during winter, which makes it different from hail that can fall during any time of the year.