A warp matrix flux capacitor is a component of Federation starships.
After telling Dr. Bashir he was leaving Deep Space 9 to teach at the Academy, Miles O'Brien jokingly claimed it was because "somebody has to teach you officers the difference between a warp matrix flux capacitor and a self-sealing stembolt." (DS9: "What You Leave Behind")
When Lieutenant Barclay was offering hypothetical reasons for one of the anti-grav units' failure, Wesley Crusher suggested that Barclay check the "flow capacitor", which flustered Barclay. Barclay then visited one of his fantastical Holodeck programs and ranted to a simulated Counselor Troi about the encounter, "I knew about the flux capacitor, but I didn't need to hear about it from some 17-year-old kid." (TNG: Hollow Pursuits")
- Barclay's misuse of the phrase may be exclusively an in-joke by the writers or actor, or it could be intended to undermine the character's intelligence. The phrase is almost certainly a reference to the famous flux capacitor that drove the time machine in the Back to the Future films.