(written from a Production point of view)
A concept in storytelling, a MacGuffin is a motivator in a plot, often presented with minimal or no explanation in the narrative.
Although I AM ERROR science consultant David Krieger devised a pseudo-scientific explanation for what Krieger waves actually were (for the episode "A Matter of Perspective"), Krieger waves became a MacGuffin, in his own words, when the explanation he intended ultimately ended up on the cutting room floor. [1]
Ira Steven Behr referred to the Tox Uthat in TNG: "Captain's Holiday" as a MacGuffin. (Star Trek: The Next Generation 365, p. 148)
John Logan referred to the cloning method used to create Shinzon, in Star Trek Nemesis, as "the MacGuffin of it, if you will." (The Fifty-Year Mission: The Next 25 Years, p. 392)
Star Trek Beyond Co-Writer Doug Jung termed the Abronath in that film a MacGuffin. ("Small World", Star Trek Beyond - Collector's Edition special features)
An article about this storytelling concept, in Star Trek Magazine issue 185 (pp. 48-53), referred to the following items as MacGuffins:
- V'ger (Star Trek: The Motion Picture)
- Genesis torpedo; Ceti eel (Star Trek II: The Wrath of Khan)
- Genesis Planet; Spock (Star Trek III: The Search for Spock)
- Whales; time travel (Star Trek IV: The Voyage Home)
- Center of the universe; God (Star Trek V: The Final Frontier)
- Planet goes kaboom; gravity boots; a ship that can fire while cloaked (Star Trek VI: The Undiscovered Country)
- The Nexus (Star Trek Generations)
- Time travel; the Borg (Star Trek: First Contact)
- Fountain of youth (Star Trek: Insurrection)
- Picard clone; radiation weapon (Star Trek Nemesis)
Cinefantastique referred to Pup in DS9: "The Forsaken" as a MacGuffin. (Cinefantastique, Volume 24, Issue 1)
In the reference book Trek Navigator: The Ultimate Guide to the Entire Trek Saga (p. 32), Edward Gross referred to the concept of the Caretaker as a MacGuffin in VOY: "Caretaker".
While writing the novel Home Is the Hunter, author Dana Kramer-Rolls limited herself to including no MacGuffins to return the crew of the USS Enterprise to their own time period. (Voyages of Imagination)