From Glossary of Meteorology
A situation that occurs in statically stable regions of the atmospheric boundary layer where turbulence is not contiguous, either vertically or horizontally.
For example, in the nighttime stable boundary layer one or more layers of turbulence can form that are separated by nonturbulent (laminar) layers. This situation is very difficult to model because the turbulence in each layer does not interact with the surface and thus can evolve separately. During daytime at the top of a convective mixed layer, there is usually a statically stable capping inversion or entrainment zone where turbulent thermals penetrating the layer are separated by regions of laminar air from the free atmosphere. Aircraft flying horizontally through this region would experience intermittent turbulence.