Simple curve in the context of "Signed area"

In mathematics, the signed area or oriented area of a region of an affine plane is its area with orientation specified by the positive or negative sign, that is "plus" (⁠${\displaystyle +}$⁠) or "minus" (⁠${\displaystyle -}$⁠). More generally, the signed area of an arbitrary surface region is its surface area with specified orientation. When the boundary of the region is a simple curve, the signed area also indicates the orientation of the boundary.