A spell cast in D&D to show the passage of time. A joke the GM can make.
The GM waves his hand across the air and says, "I cast handwavium...it's tomorrow."
a term used when a science fiction writer "waves his hands" at reality and hard science for the sake of the plot. Refers to all unrealistic or impossible technology, such as faster-than-light travel, teleportation, artificial gravity, etc.
Handwavium is extensively used in movies, more so than in literature, due to the need to mass market movies to a scientifically ignorant public and because filming realistic space travel is relatively expensive.
Star Trek is fun, but it's loaded with handwavium.
Armageddon sucked for many reasons, one of which was overuse of handwavium.
Apollo 13 didn't have any handwavium tech, it was all historically accurate hardware.