Physics

To be fair, time crystal is a real -- albeit somewhat clickbaity -- concept in physics, proposed by none other than the Nobel laureate Wilczek. In simple terms, a time crystal is something whose frequency is not a harmonic of what's driving it (e.g., its periodicity could be double that of the drive). It's a "crystal" because it's breaking the (temporal) symmetry of the governing theory, just as a conventional crystal, by forming into a lattice of atoms, breaks spatial translation symmetry.