to write or insert (words, phrases, etc.) between the lines of writing or print.

to mark or inscribe (a document, book, etc.) between the lines.

to transfer (freight) from one carrier to another in the course of shipment.

to transfer freight from one carrier to another in the course of shipment.

involving or indicating a transfer of passengers or freight from one carrier to another during travel or shipment

interline flights.

of or pertaining to transactions between competing carriers, esp. airlines, by which passengers, baggage, and freight are transferred from one carrier to another using only one ticket or one check-in procedure from departure point to destination.