These are just IATA (International Air Transport Association) codes. They are used in aviation to identify and differentiate airports. That’s why a Edinburgh Turnhouse Airport to Phoenix Sky Harbor Intl Airport flight would often be abbreviated as a EDI to PHX flight. While you’re still figuring out your travel plans, it’s not a bad idea to learn the names and codes of other airports around these areas: Phoenix-Mesa Gateway Airport (AZA), Phoenix Scottsdale Municipal Airport (SCF), Prescott Airport (PRC).