It's pretty common to use the main airport name as a synecdoche referring to the city. I regularly see CPH used instead of Copenhagen, OSL instead of Oslo, BCN for Barcelona, etc. Doesn't work for all cities, of course.
I can't say for sure, but I think CPH as airport code comes from the common abbreviation for the city, rather than the other way around. KBH (København) is also used in Danish fairly commonly, and isn't any airport's code. It's possible that KBH is a backformation from CPH, though, come to think of it. Might try to dig into that if I have some spare time.
Yeah, but how many people know where ORD is without having to think about it for a minute.
Pretty much everyone who travels often. Oh man, how I hate this airport.
Quick! What's MCO? You guessed it — Orlando.
It's a shibboleth in social media to show that you travel by air often. It's even sillier when Canadians do it because what the everloving crap does YYZ or YUL tell you if you don't already know what they mean.
its chicago. right off the bat. used to be the biggest layover place in the us. but generally CHI works too.