Quantum fluctuations are like the internet's equivalent of a 4chan meme: they're always popping up unexpectedly, never staying in one place long enough to be understood, and often making a mess.
But seriously, quantum fluctuations are the random variations in energy that appear in the vacuum of space. They're the quantum equivalent of a cosmic game of cosmic "whack-a-mole" - a particle appears, then disappears, then appears again in a different place.
Read on for more on the Fluctuation Spectrum Learn about the Heisenberg Uncertainty Principle