sleet
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sleet,
precipitation of small, partially melted grains of ice. As raindrops fall from clouds, they pass through layers of air at different temperatures. If they pass through a layer with a temperature below the freezing point, they turn into sleet. Snowflakes that have melted by passing through a warm layer will turn into sleet if they then pass through a freezing layer. Sleet often falls together with snow and rain, and may deposit an icy coating on exposed surfaces. Sleet occurs only during the winter, while hailhail,precipitation in the form of pellets composed of ice or of ice and snow, occurring at any time of the year, usually during the passage of a cold front or during a thunderstorm. Small hailstones have a soft center and a single outer coat of ice.
..... Click the link for more information. , a different form of icy precipitation, may fall at any time of the year.
sleet
[slēt] (meteorology)
Colloquially in some parts of the United States, precipitation in the form of a mixture of snow and rain.
sleet
Water droplets falling from clouds that become clear ice pellets after passing through a layer of clouds with freezing temperatures. Sleet thus indicates a temperature inversion. Sleet may also develop from the freezing of melted snow, as the latter falls through a colder layer of air near the ground. On weather charts, sleet is represented by 
sleet
1. partly melted falling snow or hail or (esp US) partly frozen rain
2. Chiefly US the thin coat of ice that forms when sleet or rain freezes on cold surfaces