Selenium

"It's a BB unit with a selenium drive and thermal hyperscan vindicator, internal self-correcting gyroscopic propulsion system, optics corrected to&mdash;"

- Rey to Kylo Ren, regarding BB-8

Selenium was a substance that could be used in the composition of drives of BB unit astromech droids. When Kylo Ren pressed Rey for details about the droid known as BB-8, she listed technical specifications such as a selenium drive, evading the real focus of Ren's inquiry: the map to Luke Skywalker that the droid contained.

Appearances

 * Star Wars: Episode VII The Force Awakens
 * Star Wars: Episode VII The Force Awakens novelization
 * Star Wars: Episode VII The Force Awakens junior novelization