There’s an old saying that goes, “It’s better to ask forgiveness rather than permission.” This doesn’t exactly apply to car usage, though. Permissive use means that you give permission to someone to drive your car. For example, you allow your roommate to borrow your car to pick up dinner. If your roommate causes an accident on their way to the restaurant, your policy would cover them because you gave them permission to drive the car. If your roommate decided to take your car without asking you, there is a chance that your policy would not cover the accident.
Permissive use applies to friends and neighbors, not your immediate family. Be sure to check with your insurance company to verify that they offer permissive-use coverage, as some of the smaller companies may exclude such coverage.