It is a one time fee the buyer pays at closing for the lender to have a third party keep track of your real estate taxes to make sure they are paid each year for the life of the loan. Your lender does not want to have unpaid real estate taxes on your property as those can become tax liens that have priority over (comes in front of) your mortgage. So the third party notifies your lender if your real estate taxes are unpaid.
What's funny is that even if you have your lender hold escrows and your lender pays your taxes each and every year, the lender still charges you a tax service fee! Fortunately it is a small amount (here it runs about $83).
