What is known shipper for air cargo?

After September 11,the United States Department of Homeland Security (DHS) implemented new rules to insure the safety of domestic and international air travel in the United States. Shippers who have been properly vetted by the Transportation Security Administration (TSA) are considered a Known Shipper and may tender their freight for shipment on both passenger and cargo-only aircraft. Any shipper who has not gone through this formal vetting process may ONLY ship freight on cargo-only aircraft and NOT on passenger flights.