 Signed area

The area of a planar oriented region with a sign determined by orientation. For a triangle with cyclically ordered points $A,B,C$, it is $\frac{1}{2}((B-A)\times (C-A))$, using the two-dimensional cross product; reversing the order reverses the sign.

The concept of "signed area" typically arises in the context of geometry, particularly in relation to polygons in the Cartesian coordinate system. It refers to the area of a shape that takes into account the orientation of the vertices (the order in which they are connected) and can therefore be positive or negative.