Your travel authorization has been approved and you are authorized to travel to the United States under the Visa Waiver Program. This does not guarantee admission to the United States; a Customs and Border Protection (CBP) officer at a port of entry will have the final determination.
It took me longer to find my passport than to get the Visa Waiver form approved. And it only costs 14$. I wonder what is the percentage of people who are not allowed admission at the port of entry?