Overview
CAPPS systems rely on what is known as a Passenger Name Record, often abbreviated PNR. When a person books a plane ticket, certain identifying information is collected by the airline: full name, address, etc. This information is used to check against some data store (e.g., a TSA No-Fly list, the FBI ten most wanted fugitive list, etc.) and assign a terrorism "risk score" to that person. High risk scores require the airline to subject the person to extended baggage and/or personal screening, and to contact law enforcement if necessary.
Read more about this topic: Computer-Assisted Passenger Prescreening System