Uninsured or Underinsured Protection
Uninsured motorist protection covers the injury and physical damage expenses of your authorized driver and any passengers in your car in an accident caused by a driver with no insurance (and, yes, there are many of them behind the wheel today!) If there is no insurance, there is very likely little chance you will collect on the injury and damage expenses incurred.
Take this a step further and you have underinsured protection for any injury and/or damage done to you, your passengers or your car by someone who doesn't have enough insurance to cover all the costs. This insurance pays the difference between the culpable driver's liability limit and your liability coverage. Think $50 a year for $100,000 coverage.
Many states do not require that you carry this kind of coverage, but most "no fault" states do.