Rene Ritchie, writing for iMore:

While Apple doesn’t use public code names for iOS the way the company does for OS X — no big cats like Snow Leopard or California landmarks like El Capitan — it does use internal code names primarily based on ski resorts. They’re not meant for the public but, once a version of iOS goes public, they’re not hard to find.

My favorite names from the list: Alpine, Jasper, and Copper.