In the 2009 film Avatar, human forces seek a valuable mineral called unobtanium on Pandora.
The mineral is the main economic reason for the human operation on the moon. The Resources Development Administration wants to mine it because the material has an extremely high value on Earth. Its extraction threatens the Na’vi’s home and becomes a central source of conflict between the mining company, the military forces, and Pandora’s inhabitants.
“Unobtanium” is an engineering joke and a long-used informal term for an idealized material that is difficult or impossible to obtain. Avatar turns that playful word into a fictional resource with a specific commercial purpose. The film’s unobtanium is also described as having unusual magnetic properties.
The term is not the same as “dilithium” from Star Trek or “spice” from Dune. Those are fictional substances from different universes. In Avatar, unobtanium is the resource that makes mining Pandora financially attractive to humans.