Definition - What does Aerator mean?
An aerator is a tool or form of gadgetry used to aerate wine. The purpose of this tool is to initiate the oxidation of wine and its evaporation via the exposure to air. In the case of some wines, those which are young and tannic, or those which have been cellar-aged for a significant period, it is necessary to aerate them in order to experience the wine in its full potential.
WineFrog explains Aerator
A wine aerator may be found in many forms, shapes and of various materials. However, there is at least one specific function that any functional aerator must have - it must have the ability to expose the wine to significant amounts of air.
With exposure to air, certain volatile compounds (aromas) have the ability to evaporate so that the consumer may appreciate the nose of the wine. For young, tannic red wines, the exposure to air will soften harsh tannins so that the texture of the wine is softer and flavors of the wine may be more apparent.
The most basic aerator for wine is a proper wine glass in accordance with the style of wine served. The glass is shaped in order for the wine to be filled just below the widest point of the glass. This allows for the wine to have the maximum allowable surface exposed to air. Filling the glass to this point also allows for swirling, allowing for more of the wine's surface area to be exposed to air. It is the similar case when speaking in terms of decanters. Alternatly, modern aerators include bottle spouts that aerate the wine as it is pored into a glass.