Freezing rain can develop in two various ways and leads to glaze on the ground. The first occur in this way: Snow falls through an area, that has positive temperatures (> 0°C), so that the snow melts. Below and down to the ground the temperatures are negative again. But instead of freezing the droplets stay liquid but get supercooled. Only after hitting on the ground the droplets freeze and form the treacherous glaze. The figure shows a sounding of a typical freezing rain weather situation.
The second way: Ordinary rain (not supercooled) impinges on a ground, that has (still) a temperature below the freezing point of water. The consequence is the same, namely that the rain freezes on the ground.