An SR-22 is the name given to a special certificate, a Statement of Financial Responsibility, that some drivers are required to carry. SR-22 certificates are purchased through your car insurance company, but it is not an insurance policy. Instead, the SR-22 indicates that you are being financially responsible and carrying the required insurance coverage for your vehicle.
SR-22 is purchased at the time of purchasing a car insurance policy. The form is generally required for people who have been convicted of a DUI, driving without insurance, or some other serious traffic offense such as vehicular manslaughter. Once the court has demanded you carry SR-22, the requirement is generally for a period of time anywhere from 1 to 5 years in length. If the SR-22 or your car insurance are allowed to lapse during that period, you may have your privilege to drive revoked or suspended.