- a function, usually expressed as a polynomial, that indicates linear combinations of the derivatives of the expression on which it operates.
- any operator involving differentiation, such as the mathematical operator del ∇, used in vector analysis, where ∇ = i ∂/∂ x + j ∂/∂ y + k ∂/∂ z, i, j, and k being unit vectors and ∂/∂ x, ∂/∂ y, and ∂/∂ z the partial derivatives of a function in x, y, and z
