means a set of equations modeling convection currents that produces a trajectory which never settles down or repeats, yet stays bounded in a strange, orderly-looking shape.

from edward lorenz, an mit meteorologist, was rerunning a weather simulation in 1961 and rounded a variable from six decimals to three, expecting no real change, and got a wildly different forecast, which he wrote up in 1963 as deterministic nonperiodic flow, later nicknamed the butterfly effect.