Filtering and Fining
After fermentation, there may still be a lot of residue floating around in the wine, which winemakers may chose remove. There are various ways for the wine to undergo 'clarification' - removal of residue, (for example, strain the wine through something like cheese-cloth, called 'filtering'), but the most common way is called 'fining'.
When making jelly, the recipes may sometimes call for adding egg whites. The materials that cloud the jelly are captured by the egg and you get a nice and bright result that looks rather pretty. It's the same with wine, even down to using egg whites. Except that the most common materials used for fining are gelatin or bentonite - a type of clay.
When and where to use heavy filtering and fining is highly debatable, since removing these substances prevents the wine from obtaining flavors from them, affecting the character of the wine. You are certain to hear complaints about "over fined and filtered wine". The implication is that such wines will have less flavor. For this reason some wines will be unfiltered.