In Orson Scott Card's Ender's Game series, an aiua is essentially the lifeforce or power from which all living things are created. Every cell is an aiua, same with a human mind. Sort of like a soul. (Although OSC would disagree) They come from Outside.
Sentient minds are aiuas that command other aiuas that compose their body. A good example of this idea is the part in Children Of The Mind where Jane's aiua enters Ender's body and tries to control his aiuas and fails. In addition to this, sentient auias are connected to each other in a kind of web. When two sentients become emotionally close, their aiuas become closer as well. So, aiuas can be considered a representation of human/sentient relationships.