I'll add that "launch editions" are also frequently labeled as "Day One" editions. This seemed to really kick off when the Xbox One was released. In this instance, the first batch of launch games were labeled as "Day One" editions. This has carried over to numerous titles to designate it was the initial batch printed or like comic books, the 1st printing. Sometimes as karyann mentioned, they included bonus dlc, booklets, etc. Sometimes, it's just a tag on cover to entice people to pick the game up, again much like comics where there is a blurb stating "Collector's item 1st issue!" or something similar.