Codename

Throughout Magic 's history, expansion sets have been given codenames when under design, well before a set's theme, identity, and lore have been solidified. This allows expansion developers and designers to work ahead further than any other section in the company, and still have terminology to refer to the set as a whole.

History
This practice was put into place starting with the Alliances expansion set; codenames for previous sets were simply the name of the set. Codenames are chosen by the head designer, Mark Rosewater. The codenames are designed to not have any connection to the mechanics of the set they refer to. They are selected before the designers even know what the set will be about.

The Masques block was the first instance of all the codenames of the sets in a block being connected; the Onslaught block was the first to have the codenames be assigned in a order, typically referencing something in popular culture. When it was announced there would be a change in the number of sets per block from three to two starting with "Blood", the codenames that had already been released for the unannounced sets became decoupled from their previous block. To make things easier internally, a new codename naming system was introduced in 2017. It follows a single theme (currently sports) alphabetically. That way everyone at Wizards of the Coast will know what comes before and after what.

Codenames for expansions
From Throne of Eldraine forward alphabetical themes are used, currently sports. Although Mark Rosewater initially said he had a list of A through Z, he later realized that sports V through Z are too difficult to name. He will change to another list after U.

Codenames for other sets
Some Core Sets, Starter level sets, Supplemental sets and extra expansions also had codenames.

Miscellaneous
Handlebar was used to refer to the "Bolas Arc" of the story, running through ten sets from Kaladesh through War of the Spark.