Fare basis, also known as fare codes, are the letters or numbers that airlines use to define the rules that are associated with different types of airfares or tickets.
What airlines (or gate agents) can or can't do for you in terms of upgrading you or making changes to your ticket is frequently controlled by the specific codes and fare basis that your ticket is based on.
Understanding fare codes are important only so that you can understand what rules are associated with the type of ticket you purchased, which can include whether or not you are able to change or cancel your reservation.
Fare Basis: a Shorthand Method of Describing Pricing Rules
The airline industry is certainly one industry that learned a long time before others the value of highly specialized pricing algorithms and pricing options. Chances are, you've probably been on an airline flight where the person sitting next to you has paid more (or perhaps less) than you have, and that's because of these fare basis codes.
In addition to dynamic pricing algorithms and strategies, which allow airlines to try and optimize seating prices based on how high the demand is for certain cities, flights, dates, times, and seats, the airlines have also used different fare basis and fare codes to differentiate all those similar seats on a single plane.
Business travelers can use these codes to understand what's available to them in terms of flight upgrades and to determine whether or not the flight they're on is going to be sold out or full. Also, instead of wasting time waiting in line for customer service, savvy travelers who know how to read the fare basis code can quickly assess whether or not they can get bumped up to a better seat.
Cracking the Code
Fare basis (or fare codes) are typically identified by a character, such as F, A, J, or Y. For example, letters such as "L, M, N, Q, T, V, and X" usually refer to discounted economy class tickets, while code such as J and C refer to business class and F to first class.
Usually, after the first letter specifying the fare class (such as Q or Y) is another set of characters. These follow-on characters usually specify other characteristics of the ticket, such as refundability or minimum stay requirements. Some airlines only have one or two characters (such as "YL") while others have more.
Your itinerary may contain multiple fare codes if you have multiple flights booked. However, keep in mind that if you have an itinerary made up of multiple fare codes, you may be restricted by the limitations of the most rule-bound portion. So, if one segment of your journey is non-refundable, and the next segment isn't, the entire ticket may be non-refundable. It's best to check with your travel agent or airline representative to know for sure.