Quasineutrality (${\sum }_s{q}_s{n}_s\simeq 0$)

On spatial scales much larger than the Debye length, a plasma may have nearly cancelling positive and negative electric charge densities while still carrying an electric current and having a nonzero electric field. Quasineutrality is an approximation on appropriate slow macroscopic scales, not an assertion that each fluid element has exactly zero charge or that charge separation can be ignored at every boundary.