On a statement of income I see an item that says Interest on Mortgage Payable. What is this and is it a recurring amount every year?

Let's say you want to buy a house for $500,000.

You pay for it with $100,000 of your own money and you take out a bank loan for the other $400,000.

That mortgage of $400,000 will run for about 30 years and in that time you will pay back both the principle PLUS interest.

So interest payable is just that, the repayment of the loan with interest.

And yes it is a recurring amount, but it is not always the same amount since the overall balance keeps shrinking every time you make a payment.