Aura is the life energy one possesses. It can be used in many ways. It can affect others. There are different kinds of aura... i.e. fighting aura. Some cartoons exaggerate this, showing glowing shadows of power. It can be used with magical properties. One can transfer an aura into one, thus giving them more power/energy.
Vegeta powered up, his aura bursting in a golden plume of power and light.