Freezing rain is rain that falls through a shallow layer of freezing air near the ground and freezes when it touches surfaces. The droplets remain liquid while falling, even though they have cooled below 0°C, making them supercooled.
This usually happens when snow melts into rain in a warm layer of air above a colder surface layer. If the cold layer is deep enough, the drops freeze before reaching the ground and become sleet, also called ice pellets. If it is shallow, the drops remain liquid until impact, producing freezing rain.
Freezing rain can coat roads, trees, power lines, cars, and aircraft with a smooth layer of ice called glaze. A major storm dominated by this precipitation is often called an ice storm. It is commonly confused with sleet, but sleet arrives as solid pellets, while freezing rain arrives as liquid drops.