Fare Class
What is Fare Class?
A fare class is the single letter attached to your ticket that identifies which fare you actually bought. It sits beneath the cabin: two people in adjacent economy seats can hold different fare classes and therefore different rights to change, refund, upgrade and earn miles. It is also called a booking class or booking code.
The letter is the operative part of the ticket. Cabin tells you where you sit; fare class tells you what the ticket can do. It determines whether a change costs a fee or nothing, whether a refund is possible at all, how many miles the flight earns, whether the ticket can be upgraded with points, and where you sit in the queue when a flight is cancelled and everyone needs rebooking.
A few letters are broadly conventional across airlines: Y for full-fare economy, J for full-fare business, F for full-fare first. Almost everything else is airline-specific, and the same letter can mean quite different things on two carriers. This is the honest answer to what a particular code means: there is no universal table, and the only reliable source is the fare rules attached to your own booking, which is where searches for a specific letter should end up.
The reason so many letters exist is that airlines sell the same cabin at many prices at once, each in its own bucket with a limited number of seats. Cheaper buckets sell out first, which is why the price rises as a flight fills rather than because of anything you did. It is also why an award seat can be unavailable on a half-empty aircraft: the award bucket is closed even though the cabin is not full.
Where this becomes practical is at booking. Two economy fares differing by a small amount are often in different classes, and the more expensive one may be changeable, may earn full miles, and may be upgradeable, while the cheaper one is none of those. On a long or uncertain trip that difference is usually worth more than the saving. See frequent flyer for how classes translate into miles and baggage allowance for the other entitlement the fare decides.
On a codeshare, the class is set by the airline whose ticket you hold, while the service is delivered by the airline operating the flight, which is a common source of surprise about meals, seats and miles.
Example of Fare Class
Theo booked the same route twice in the same cabin, once well ahead and once at the last minute, and paid slightly less for the later ticket. When the miles posted, the cheaper booking had earned a small fraction of what the earlier one did, because the two seats were sold in different buckets. The aircraft, the route and the legroom were identical. The letter on the ticket was not, and that letter was the only thing that decided what the flight was worth to him afterwards.