the term pnr was originaly [ in the 60's] the record of a passangers name , address, phone #. it was a separate file from the seat inventory which was a count of seats sold [reserved] & availabilty on each class on each flight . seats were assigned at checkin. now all info is in a record[s] accessable by a record locator [ 6 character ] i don't know what the proper name is for this record [ may vary by system] but pnr is understood as a reference for this record .