An SR-22 is a document that shows proof of your financial responsibility. If you're caught driving without insurance, you'll be required to carry an SR-22 for a specified period of time, normally three years. This normally occurs after a DWI, DUI, serious moving violation, at fault accidents (without insurance), repeated traffic offenses in a short time period, license suspension or revocation.
An SR-22 is filed with the state to prove that you carry car insurance for a specified period of time, similar to a probationary period. You must carry continuous coverage for this time period, and if your policy is lapsed or suspended, the insurance company will immediately notify the state, and your license will be suspended. Many states have a minimum amount of coverage that must be maintained with an SR-22 status.