What exactly is BI, UM and PIP coverage? And what do they mean if I have been in a car accident?

I'm confused about the different types of coverage listed on my automobile insurance policy.  

Bodily Injury Insurance

BI stands for 'bodily injury .' This type of coverage will pay claims for injury you negligently cause to another as a result of the use of your vehicle. Washington state law requires that every driver carry insurance for bodily injury with policy limits of at least $25,000.

Under-Insured / Un-Insured Motorist Coverage

UM stands for 'uninsured motorist' or 'underinsured motorist .' If you are injured by a negligent driver who does not have liability insurance (or inadequate liability insurance), you may make a claim with your own insurance carrier if you have UM coverage. When you make a UM claim, your insurance carrier "stands in the shoes" of the negligent driver and is permitted to assert all defenses that this driver may have had against you (e.g., comparative fault, excessive medical treatment, etc.).

Personal Injury Protection Insurance

PIP stands for 'personal injury protection .' PIP pays for your reasonable and necessary medical expenses, regardless of who is at fault for the collision. Although the law does not require that you carry UM and PIP coverage, insurance companies must offer these types of coverages to you. If you choose to reject UM and PIP coverage, your insurance company must record your rejection in writing. An insurance company's failure to obtain your written rejection of UM or PIP coverage prevents the carrier from denying the claim, even if you didn't specifically pay for this type of coverage.