Gap insurance covers the excess amount on your auto loan in an instance where your insurance company does not cover the entire loan. Depending on the companies specific policies it might or might not cover the deductible as well.
This coverage is marketed for those who put low down payments, have high interest rates on their loans, and those with 60 month or longer terms. Gap insurance is typically offered by your finance company when you first purchase your vehicle.
Most auto insurance companies offer this coverage (gap insurance) to consumers as well. If you are unsure if gap insurance coverage had been purchased, you should check your vehicle lease or purchase documentation.