What's the difference between home_url() and site_url()

Question

My understanding is that site_url() returns the location where the wordpress core files are.

So, if my blog is hosted at http://example.com/blog then site_url() returns http://example.com/blog

But then how does home_url() differ? For me, home_url() returns the same thing: http://example.com/blog

If that's correct, then can I get wordpress to return http://example.com/ ?