What is back-to-back ticketing?

Back-to-back ticketing is the practice of nesting one ticket inside another for the purpose of saving money. For example, let’s say the traveler needs to be in London Tuesday through Thursday of week 1 and again in week 2. Instead of buying a ticket for week 1 travel and a ticket for week 2 travel the traveler might want to book one ticket to travel NYC to London on Monday of week 1 and return London to NYC on Friday of week 2, and a separate ticket to travel London to NYC on Friday of week 1 and NYC to London on Monday of week 2. While this will sometimes save money, the airlines prohibit this practice: “(airline) prohibits, and Travel Service Provider is liable for, any booking or ticketing practice that circumvents the applicable Fare Rules, including but not limited to Back-to-Back Ticketing, Throwaway Ticketing….” To enforce this prohibition the airlines reserve the right to cancel any such reservation and apply financial penalties to the travel service provider (Travel-On).