The meaning of these codes is not often known by the passenger, but conveys information to airline staff; for example, they may indicate that a ticket was fully paid, discounted, part of an excursion package, or purchased through a loyalty scheme.
[3] Booking codes are the identifiers used by the airline's revenue management department to control how many seats can be sold at a particular fare level.
Some codes cannot be sold by agents, and those seats may be reserved for international connections, loyalty programs, or airline staff relocation.
These restrictions can include, but not limited to: which is published in legalese such that it can be validated automatically by global distribution systems.
It is commonly presented as a single line with standardized codes[7] which can be used for travel agents to price the ticket in global distribution systems.
It is common for a multi-sector air ticket to have more than one fare basis, particularly if it is for carriage on more than one airline, or different classes of travel are involved.