NEW YORK — 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 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.

Why are the codes there?

Airline tickets weren’t always so complicated. Codes were developed as the airlines created complex systems that let them make more money per ticket.

The fare basis code is found on most e-tickets by itself, but it can also be shown as the first letter of a longer code with a mix of other letters and numbers.

The rundown

The good news: The better code you have, the better your chance of not getting bumped. You also might receive more frequent flier miles if you’re in the top tiers. The bad news: The main way to improve your code is to pay more.

Most leisure travelers wouldn’t think of forking over double or triple the usual fare for a refundable ticket or more perks. But there are ways to avoid hassles without paying through the roof.

One way to prevent bumping with a discounted ticket? Check in early. In addition to ranking by price, airlines also prioritize passengers by check-in order. Get in the habit of checking in online 24 hours before your flight. You can even check bags online through most airlines, and just drop them off at a counter when you arrive at the airport.

But fare classes aren’t just important when it comes to keeping your seat. Fare classes are also key if you want to upgrade your ticket. Generally, “Y,” “B” and “M” are the only coach fares that are upgradeable. You can search by fare class directly on most airline websites.

If building up frequent flier miles is important to you, avoid auction tickets on sites such as Hotwire and Priceline where you name your own price, or don’t see all the flight information before you book. Those tickets, like Hotwire “Hot Rates,” are often ineligible for frequent flier miles.

The cheapest tickets doled out to certain travel agents also aren’t always eligible, either. It’s important, in these cases, to always read the fine print.