Cloud Point

Definition
The cloud point of a clear distillate fuel is the temperature at which the fuel becomes cloudy because of the appearance of wax crystals. 
In the ISO Standard 8217 cloud point is only prescribed for DMX grade, "bright clear" distillate fuels for emergency diesel and lifeboat engines. Compliance with this parameter ensures that the fuel is suitable for use in ambient temperatures down to -15oC without heating the fuel.
If a distillate fuel has a high cloud point and the engine is operating in cold climates wax crystals will form which can lead to fuel starvation and failure of the engine.