or rotation, n. a vector quantity, written ∇ × A, curl A, or rot A, associated with a vector field that is the vector product of the operator
∇ = i ∂/∂ x + j ∂/∂ y + k ∂/∂ z
with a three-dimensional vector function A, where i, j, k are mutually perpendicular unit vectors, and ∂/∂ x, etc. are the partial derivatives of A.