An integral involving two or more integrations with respect to different variables, where the integrations are carried out sequentially and variables other than the one being integrated are treated as constants. A double integral is the special case where two integrations are involved. Multiple integrals can be definite or indefinite. For example,
This double integral represents the volume under the plane z = x + 3y + 5 that lies above the rectangle 0 ≤ x ≤ 2, 0 ≤ y ≤ 3.