A datacard containing the Death Star plans
A data disk, also referred to as a datacard or datadisc, was a portable, flat device for storing data. These devices were often used to store chain codes.
During the events of the Battle of Scarif, the Death Star plans that Rogue One had managed to steal were transmitted to the Profundity, at which point they were then copied to a datacard. This card was then entrusted to Princess Leia Organa, who subsequently attempted to get the plans to Obi-Wan Kenobi on Tatooine. When her vessel came under fire from the Imperial I-class Star Destroyer called Devastator, she placed the datacard within the memory banks of R2-D2, after quickly recording a message intended for Kenobi.
Within the non-canon video game Star Wars: Galaxy of Heroes, datacards are present as an in-game item. They contain characters and other materials, and vary in value from bronzium to chromium packs, and the most valuable aurodium.