What does APR mean for a home mortgage?

Would someone explain to me in plain English (think "Mortgages for Dummies" here) what is included in APR?
Update: I know what APR stands for and everything. What I'm interested in is what is included in the APR that brings my rate from something like 6.5 up to 6.7? That seems like a lot of money over 30 years so I want to know what I'm paying for.
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