Slush is a slurry mixture of snow and liquid water. In the natural environment, slush forms as ice or snow melts. This often mixes with dirt and other materials, resulting in a gray or muddy brown color. Often, solid ice or snow will block the drainage of fluid water from slushy areas, so slush often goes through multiple freeze/thaw cycles before completely disappearing. In areas where road salt is used to clear roadways, slush forms at colder temperatures than it would ordinarily, and only in salted areas; this can produce a number of different consistencies over the same geographical area.
Slush can be a problem on aircraft runways as the effect of excess slush acting on the aircraft's wheels can have a retarding effect during take off, causing accidents such as the Munich air disaster.