There are a few ways that a one-sided dime could have been produced. One possibility is that the coin was struck twice. This would cause one side of the coin to be blank. Another possibility is that the coin was struck off-center. This would cause one side of the coin to be nearly invisible.
One-sided dimes are considered to be very valuable. In 2017, a one-sided 1966 dime sold for over $100,000.