An airport code, also known as location identifier is a station code or simply a location identifier, is a three-letter code designating many airports around the world. The characters prominently displayed on baggage tags, Air Way Bills, Tickets, Barcode Labels etc.
In early 1930s, the pilots from USA used a 2 letter code from National Weather Service (NWS) for identifying cities. This system became unmanageable for cities and towns without an NWS identifier, thus a three-letter system of airport codes was implemented. This system allowed for 17,576 permutations, assuming all letters can be used in conjunction with each other.
In large metropolitan areas, airport codes are often named after the airport itself instead of the city it serves, while another code is reserved which refers to the city itself. Sometimes, a new airport is built, replacing the old one, leaving the city's new "major" airport code to no longer correspond with the city's name. Some airports are identified even in colloquial speech by their airport code. The most notable example is LAX.