Definition - What does Filtering mean?
Filtering is a process by which wine is pumped or "pushed" through a filtering pad or screen in order to remove any residual grape particles. Wines can be filtered for their stability and clarity. Depending on the winemaker, they may desire to only filter the wine in order to remove particulates which cloud the wine.
WineFrog explains Filtering
The depth of filtering a wine is decided by the winemaker, and further filtering via a filtering pad on a micro-level to remove other particulates (i.e yeast cells) often strip the wine of finer flavors and complexity. The method of filtering, whether it will it is performed or not, is determined by the style of wine.
The first method of filtering is "racking". It is performed by allowing the sediment of a wine to precipitate to the base of its holding vessel. It is then carefully pumped from the holding tank to another empty vessel, leaving the solid particulates behind.
Another method following racking is to filter the wine by using filter pads or membranes to trap smaller particulates.
Cold stabilization is another form of filtering, often used more specifically for white wines that can loose complexity via a membrane filter. The process essentially drops the temperature of the wine to cold temperatures which allow for particulates, such as tartaric acid, to precipitate from the wine.