A "slicer" was an individual who specialized in slicing into computer systems and programs, and breaking encryption.
Nine months after the First Battle of Geonosis, scientists working for Separatist leader Count Dooku successfully sliced into the Republic HoloNet by seeding the spaceways with hyperwave transceiver nodes of a novel design. Dooku used this access to the HoloNet to broadcast propaganda Shadowfeeds.
A Weequay slicer stealing data on the TIE/d Defender.
Eight years after the rise of the Galactic Empire, on the planet Gorse the explosives expert Skelly built all his computers from kits so that they were safe from slicing while he gathered evidence that the Empire's continued mining on Gorse's moon Cynda would result the moon being torn apart. Zaluna Myder, a shift leader for the surveillance company Transcept Media Solutions on Gorse, was capable of slicing into various Imperial systems. When Myder joined Skelly, Kanan Jarrus, and Hera Syndulla on a mission to stop Count Denetrius Vidian's plan to destroy Cynda, she was able to slice into surveillance and communications systems and carried devices that helped her do so. However, when they had the opportunity to explore files downloaded from Vidian's cybernetically enhanced brain, Myder was unable to decrypt one of the files, claiming she was not a slicer. When confronted by Vidian, Myder's equipment fell out of her bag, leading the Count to believe she was indeed a slicer.
Sabine Wren possessed slicing skills. Master Codebreaker and DJ were also professional slicers, with the latter being able to use a slicer virus for his works. The Centrist senator and First Order agent Carise Sindian also apparently employed the services of at least one skilled slicer, whose services she used to frame her opponent Senator Ransolm Casterfo, making it appear as if he had ties to the Amaxine warriors.