What is Aura of Good?

[jyster]

Here is the ability

Aura of Good (Ex): The power of a paladin’s aura of good
(see the detect good spell) is equal to her paladin level.

[Ryu Kaijitsu]

I think it only matters for Detect Alignment abilities and spells

[Shadowborn]

Ryu is correct. Look at the chart at the bottom of this page or the corresponding entry for the spell in the Core book. Paladins, as direct agents of good, have a stronger aura than your average person of LG alignment, who more often then not won't register with that spell at all unless they're mid-to-high level.