An SR-22 is basically a form which must be filed by the insurance company to show the state or court that a person has auto insurance liability in effect. It is typically required of a motorist who has been involved in an accident or convicted or a traffic offense and was unable to show financial responsibility. It also can be required as part of the license reinstatement process in some states.
If you are required to obtain a SR-22 form or certificate of financial responsibility in this way and do not own a motor vehicle, you can obtain a Non-Owners SR-22. A non-owners SR-22 generally allows the named insure to drive any vehicle that they are given permission to drive by the vehicle owner, unless the vehicle is owned by a household member.
So the different between a normal SR-22 and a Non-Owners SR-22 is that with a Non-Owners SR-22 policy you do not own a vehicle to directly insure. While with a SR-22 policy you own a vehicle in which the insurance is put on.