Racking

This process ultimately helps leave sediment behind. For aeration or clarification. Can be helped by using fining agents. Racking can occur some three or four times before a wine is clear. Even after racking, some wines may be filtered to remove any left over particles.

Quite simply, racking is to move the stuff you want (wine) away from stuff you don't (yeast, sugar, skin, stem, other stuff which isn't liquid). The crazy thing about this process is that they could be removing wine from such particles as ox blood or egg whites....... see FINING.