An uninsured or underinsured motorist claim is one that you file to your own insurance company because you experienced damages in an accident caused by a driver or vehicle that wasn't covered or fully covered. If you have the proper uninsured or underinsured additions on your own policy, the theory is that your insurance company should pick up the slack and help you cover your losses.
A lot of parameters govern whether you'll be successful with such an approach, though. For example, not every accident you are involved in with an uninsured or underinsured vehicle is allowed under most of these policies. If you are in an accident that involves another vehicle that is owned by someone in your family or yourself, then your uninsured motorist policy will likely not apply. This is true even if the car in question is not fully covered.
Vehicles that are self-insured are also usually reasons that an underinsured policy won't pick up any losses. The one time this isn't true is if the self-insured person ends up going insolvent and is unable to meet the obligations of his or her self-insured arrangement.
Other types of vehicles that can put a lid on your uninsured or underinsured policy includes government-owned vehicles, vehicles that are designed for use in off-road activities only or which are being used off-road at the time of the incident and vehicles that are being used as a residence, such as mobile homes or RVs that are being maintained in a park environment.
You also can't usually tap your uninsured motorist policy if you are involved in an accident with a vehicle that is meant to be used on the railways and not the roadways. If you are involved in an accident and want to know what your options are for seeking compensation, consider speaking with a personal injury lawyer.
Source: American Institute of CPAs, "Uninsured/Underinsured Motorist Coverage," accessed Feb. 24, 2017