Beltrami Field

A Vector Field u satisfying the vector identity

$${\bf u}\times(\nabla\times{\bf u})={\bf0}$$

where ${\bf A}\times{\bf B}$ is the Cross Product and $\nabla\times{\bf A}$ is the Curl is said to be a Beltrami field.

See also Divergenceless Field, Irrotational Field, Solenoidal Field