Amortization as an Add-Back?

In our world, so much depends on valuing a company well. And usually I look at some combination of discounted cash flows and EBITDA. I've bought a couple companies now but there's still something I don't understand. When you see "amortization" in the add-backs is that amortization of some asset the business has or some loan? I have seen sellers and brokers try to add-back both but the amortization dollars to pay off a loan are already captured in the starting point of net income. So that makes no sense to me and it appears they're double counting it toward EBITDA. If it's the former, that makes some sense I guess. The reason I asked this is that I recently saw a CIM with huge add-backs and thought I'd bring the point up before a bunch of smart minds.