Have you ever notice all the alphabet soup on your airline reservations or online itineraries? If you are flying from New York to Los Angeles, why doens't it just say so Instead of JFK-LAX.
Same holds thru when you check your luggage. Ever notice those little tags they stick on the side or elastic band onto the handle with a 3 letter code?
All those 3 letter codes you see are called IATA Airport Codes. (That's the International Air Transport Association). This system for identifying airports quickly and easily was started WAY back in the 1930's by pilots. The National Weather Service had assigned a 2 letter code to most major cities. Pilots started adopting this lingo to shorten their communications in the same way we use abbreviations like OMG when texting now. Most of the airports back then were in large cities anyway. For example, the National Weather Service called Los Angeles LA and pilots put their own aeronautical spin on it by ending with an X. So that is how we got airport codes like LAX or PHX for Phoenix.
As air service, populations and airports grew, things became a lot more complicated. This is why IATA stepped in to standardize all the airport codes and the lingo that everyone uses in the air industry.
Many airport city codes are fairly straightforward...Boston is BOS, Miami is MIA and Atlanta is ATL. Then it gets a bit more complicated.
The letter N can only be used to designate NAVY air fields. That is why New Jersey's Newark airport code is EWR and not NEW. Regional airports often combine the letters of the areas they service like MSP for Minneapolist/St Paul of DFW for Dallas/Fort Worth.
Other airport codes seem like they have absolutely nothing to do with the name of the city or region like Nashvile BNA. The airport there is named after Col. Harry Berry who helped to get the airport built at Berry Field. Orlando MCO airport was formerly a McCoy Air Force based before it became a civilian airport.
For really large Metropolitan areas with multiple airports there are airport codes that combine even larger areas. For example, some reservations systems will allow you to search for airfares using the code NYC instead of specifically search for flights from Kennedy Airport JFK, LaGuardia LGA and Newark EWR.
Another crazy part of this airport code naming system is that the first and second OR second and third letters of any airport code cannot be the same as any other airport within 200 miles.
Confused! well, just imagine there are codes for the thousands of airports all around the globe.