Have you ever looked at your baggage tag, seen the three-letter airport code and wondered what it meant? Some, like SFO — San Francisco International Airport — make perfect sense, while others, like PIE — St. Pete-Clearwater International Airport — are less intuitive. Airport codes can seem unusual at times, but they all have a meaning and in most cases a good story to tell. The International Air Transport Association, which advocates on behalf of the world's airlines, oversees and creates these airport codes. Below you'll find a list of 10 airports with unusual codes and an explanation of how they were created.

Chicago O'Hare International Airport: ORD

Chicago O'Hare, our home base, was originally known as Orchard Field Airport. It was renamed in 1949 to honor local Medal of Honor recipient Edward O'Hare, the Navy's first flying ace during World War II. OR comes from the first two letters of Orchard, and D comes from the last letter in Field, making up the airport code ORD.

Beijing Capital International Airport: PEK

Beijing's airport code comes from the first three letters of Peking, the original English translation of the name of China's capital city. United began flying to Beijing in 1986, with service now available from Chicago, New York/Newark, San Francisco and Washington D.C.

Orlando International Airport: MCO

The gateway airport to Central Florida was originally home to the McCoy Air Force Base, named after Colonel Michael Norman Wright McCoy, who was killed in a jet crash in 1957. After the base closed in 1975, it became Orlando's main airport. The M, C and O come from the name McCoy.

Louis Armstrong International Airport, New Orleans: MSY

The New Orleans airport was originally named Moisant Field after John Bevins Moisant, an aviation pioneer. The airport is located on what was previously known as Moisant Stock Yards, hence the MSY airport code. It was renamed Louis Armstrong New Orleans International Airport in 2001 to honor the jazz musician's 100th birthday.

Guam International Airport: GUM

This United hub was originally built by the Japanese as a military base in 1943. Its name comes from three of the four letters of the country's name.

Sioux Gateway Airport, Iowa: SUX

Before embracing its airport code, Sioux City tried several times to get what it saw as an offensive designator changed. But after seeing alternatives, it decided to embrace the code and turn it into a marketing tool. The Sioux City Airport now sells merchandise using the "Fly SUX" brand.

Singapore Changi Airport: SIN

There's nothing sinister about this airport's code, derived from the first three letters of the island city-state's name. It has been named the world's best airport for the past four years by the Skytrax ratings.

Fresno Yosemite International Airport: FAT

This airport's code has nothing to do with its size. The gateway to California's iconic national park got its airport code from its original name: Fresno Air Terminal. When the airport took on its current name in 1996, it applied to the Federal Aviation Administration for a new code, but it was turned down. The FAA only gives out new codes when an airport moves from one location to another.

Madrid–Barajas Airport: MAD

The code for the Madrid airport is pretty simple. It's the first three letters of Spain's capital and most populous city. The Barajas part of the name comes from the district located near the airport, which is considered a gateway to the rest of Europe and the world.