Maceration is the winemaking process where the phenolic materials of the grape—tannins, coloring agents (anthocyanins) and flavor compounds—are leached from the grape skins, seeds and stems into the must.
Cold maceration is skin contact before the beginning of the fermentation process. Some winemakers allow the skins to remain in contact with the must after fermentation is finished. This is known as extended maceration.
Carbonic maceration allows grapes to ferment without intentionally breaking the skins. Must is the mixture of solids and grape juice before fermentation begins. Up to a quarter of the must is skins and other debris, known as pumice. The amount of contact with these solids is one of the major ways a winemaker can craft the wine.
(Source – Calwines.com, UC Davis)