15 year Term, 20 year Amortization. Define Amortization?

[Andrew Michaud]

I have been approved on a loan for 15 Yr, 20 Yr Amortization. What does this mean? 

Am I paying off the loan in 15 years or 20 years?

Am I paying off the interest in 15 years and paying off the rest of the principal from year 15 to 20?

Have done some research but still cannot figure this one out.