Oxygenation or aeration is the process of adding oxygen or air to your fermentation temperature wort to increase the oxygen content.
This is important because, during the growth phase of the fermentation, the yeast cells replicate their numbers ready for active fermentation. Oxygen is needed for cell wall production and replication. This allows for a healthier fermentation because the yeast is healthier. The goal for oxygen content is about 8-10 ppm or about 60 seconds of pure oxygen bubbled through the wort or 20 minutes of aeration.