Somebody runs a light, you are hurt, and they have no bodily injury liability, which as Florida law stands they were never obliged to buy. Their policy pays you nothing for your injuries. This is the coverage that steps into that silence.
What it actually pays
Uninsured and underinsured motorist coverage pays for your injuries, your lost income and your pain and suffering when the at-fault driver has no bodily injury liability at all, or has too little to cover what they did. It follows you rather than the car, so it applies as a passenger in someone else’s vehicle and, on most policies, as a pedestrian.
PIP does not do this. PIP pays a share of your medical bills up to a low limit and stops well short of the rest. On any injury beyond the minor, the gap between what PIP pays and what the crash costs is the whole question, and this is the only coverage on a standard auto policy that answers it.
Stacked, unstacked, and why it matters
Florida lets you buy the coverage stacked or unstacked. Stacked multiplies your limit by the number of vehicles on the policy; unstacked holds it at one limit however many cars you insure. Stacked costs more and is worth more, and a household with three cars is making a larger decision than it usually realises when it signs the rejection form.
That rejection form is the thing to know about. Carriers must offer the coverage and you may decline it in writing, which many drivers do at a dealership desk without registering what they signed. If you are not sure which way yours went, we can read your declarations page and tell you.