What is a Bard and what do I do with it?

I was told a while back that Bard wasn't supposed to be a bot lane support. He was supposed to be an every lane support.

Well, I still don't get how that's supposed to work and, though I like the idea of being able to support all lanes at once, I've yet to see this done.

How am I supposed to use Bard to make this work?