Freezing rain is rain that comes down in rain droplets as liquid and then freezes when the rain hits the ground or other cold surface.
The rain is not actually frozen when in the air like sleet is and when it's freezing rain out the freezing rain will remain liquid until it hits the ground or your windshield, cars surface etc.
The sleet is precipitation consisting of ice pellets which is often mixed with rain or snow.
The sleet can sometimes occur and form on the ground like snow does.
Sleet is frozen while it's coming down from the sky above but freezing rain is only frozen when it reaches earths surface.
Freezing rain and sleet can sometimes look and seem similar but they are different.