Definition - What does Supercooling mean?
Supercooling, also called undercooling, is the process by which the temperature of a liquid or gas is lowered below its freezing point without turning into a solid. In the case of winemaking, supercooling is synonymous with cold stabilization. This is the process in which wine is rapidly chilled to freezing temperatures without becoming solid in order to stop fermentation.
WineFrog explains Supercooling
By supercooling (cold stabilizing) a wine during fermentation, a winemaker is able to stop fermentation. The freezing temperatures will kill the active yeast cells. The frozen yeast cells, along with other solid particulates will then eventually fall to the bottom of the holding tank.
This is another form of fining when the process of filtering wine is less-desirable. Supercooling is more reserved for white and rosé wines as they are more delicate and certain aromas and flavors can be lost if they were to be fined/filtered through a plate filtering system.