I like what Jiminy Cricket says when Pinocchio asks:
Pinocchio: What are conscience?
Jiminy Cricket: What are conscience! I’ll tell ya! A conscience is that still small voice that people won’t listen to. That’s just the trouble with the world today…
I like to also relate it to “the force” in Star Wars. In the end I think it mostly comes down to love – it’s the heart of your inner being that reminds you what the “right” thing to do is – the thing that will demonstrate the greater love.
It is also the voice of God.