Phlebotinum

Often the substance is completely unexplained beyond its names and the countless applications it has, but it is rarely explained what its actual properties are.

Real world examples would be water and petroleum (oil) if there ever was scarcity for them (current future predictions indicate there will be in a few hundred years). As these are used in pretty much everything there is (and if there's something that doesn't contain either, you can bet these were used in the production of whatever that is somewhere along the line).

See also: fictional element, object plot