Maceration refers to the period of winemaking in which the must (aka juice) is in contact with the skins, stems, and seeds. These impart the important tannins, coloring agents, and flavor compounds that are necessary for some wines, especially red wines. White wines typically do not go through this process. Extended maceration is when seeds and skins of grapes are left in contact with juice or wine for a longer period of time than what's "typical". The goal of extended maceration is to increase color, flavor, and tannin structure in the wine.