One letter on a plane ticket says a lot about you

There are a few bits of information to pay close attention to on an airline ticket: the flight number, gate number and boarding time. Fare basis code? Not a common concern.
But the single-letter code can make a big difference in some parts of the travel experience, even though most passengers don't pay any attention. A fare basis code further divides passengers into classes based on how much they paid and how far out they booked. There are about a dozen in coach class alone.
When you're on the plane, there's no difference in service between a passenger who has a "Y" or "Q" — a full-fare and a discounted ticket — if you're both in coach. But the codes are still important: Some indicate your trip isn't eligible for frequent-flier miles or an upgrade; others tell a ticket agent where to rank you on a standby list.
Deciphering the code
The letters airlines assign to certain levels of coach can vary widely, but a couple are universal. "Y" class is a widespread denotation for the highest class in coach among most major airlines, according to Jami Counter, senior director of TripAdvisor Flights and a former pricing strategist at American Airlines. These tickets are usually fully refundable, last-minute coach fares purchased mainly by business travelers. They're the most expensive tickets, but they have the most flexibility.
Some others that are generally used among the airlines: "J" or "C" usually indicate business class. "F" and "P" denote first class or premium. LINK