Allowing Wine to breath (as it is sometimes referred to) is allowing it to be exposed to air after opening. Aerating red wines and some white wines releases the flavor and bouquet which is a simple way to vastly add to the pleasure of drinking wine
Good - Aerator at the end of the bottle:
An aerator at the end of the wine bottle; Insert the aerator directly into the end of the wine bottle. As you slowly pour wine into your glass, it is exposed to air inside the aerator, causing oxygenation which increases its scent and flavor. These aerators provide oxygenation with convenience and are perfect for those who don't have the time to decant with a decanter or do not have a decanter available.
Better - Decanter
Empty your bottle of wine into your decanter and wait at least 30 minutes before serving.
Best - Decanter with an Aerator:
Insert the aerator for decanters into your decanter, and then slowly pour a bottle of wine into the aerator. As the wine travels through the aerator it is forced through small holes which spray the wine throughout the decanter. Because all of the wine has been exposed to air using this enhanced method of aeration, it provides instant and maximum oxygenation to the entire bottle. With this type of aeration, you don't have to wait to enjoy your wine; it is ready to be served immediately after decanting.