Kelvin-Helmholtz instability is a fluid or plasma instability that forms when neighboring layers move at different speeds. The shear at their boundary can trigger waves, rolls, and mixing instead of a smooth interface. In ordinary fluids this can be seen in clouds, ocean surfaces, or smoke; in plasma it can also interact with magnetic fields and change how energy and particles move.
In cyber security, the term is not an attack method, but it matters in the physical systems that support secure communications and infrastructure. Space-weather models, satellite operations, and some laboratory plasma systems use this physics to predict turbulence, signal disturbance, or equipment stress. Defenders and engineers study it to understand when fast-moving layers may become unstable and disrupt sensors, antennas, or high-energy hardware. In practice, it is a reminder that security sometimes depends on the behavior of the physical environment, not just software.