RPM Package Database vs YUM Software Repository

Hello everyone... Another question.. I've learned first of how to use RPM, then following that, I learned about YUM. From the wording of the book I'm using, it makes sound like both databases are for packages. Would that mean that they are both the same thing? when you download a .repo it's stored in the /etc/yum.repos.d directory. and that is used when you want to YUM isntall or YUM upgrade something right?

So what resides in /var/lib/rpm ? Is this directory used to the same effect? This time made use of when using RPM -ivh?

I apologize for the low level questions, but trying to get a grasp on this..