"Any sufficiently advanced technology is indistinguishable from a completely ad-hoc plot device"
Phlebotinum is the versatile substance that may be rubbed on almost anything to cause an effect needed by a plot.
Some examples:
nanotechnology, magic crystal emanations, pixie dust, a
sonic screwdriver, or even just some
Green Rocks. In essence, it is plot fuel. Without it, the story would grind to an abrupt halt. It's science, it's magic, it's strange things unknown to science or magic. The reader does not know how Phlebotinum would work and the creators hope nobody cares.
According to
Joss Whedon, during the DVD commentary for the pilot episode of
Buffy the Vampire Slayer, the term "phlebotinum" originates from
Buffy writer (and
Angel co-creator) David Greenwalt's sudden outburst: "Don't touch the phlebotinum!" apropos of nothing.
* Whether or not he had the etymological connection in mind, "phlebotomy" is the drawing of blood, coincidentally appropriate in context.
If the phlebotinum in question is simply a physical substance with unusual/extreme properties you are almost certainly dealing with the element
Unobtainium.
A.K.A. Handwavium. Compare
MacGuffin,
A Wizard Did It,
Hand Wave, and
Deus ex Machina. Contrast
Misapplied Phlebotinum
Tropes
Applied Phlebotinum is among the
Tropes Of Legend.