An Aura is an optical effect wherein gas or dust surrounding an object luminesces or reflects light from the object.
The visual disturbances seen by approximately 50% of migraine sufferers is also called aura.
Figuratively, an aura refers to the character of concepts/issues/phenomena surrounding a particular topic. eg: 'The discussion had an aura of casualness'.
AURA is also an Acronym for: Association of Universities for Research in Astronomy