Mouth
A Principal Vertex 
of a Simple Polygon 
is called a mouth if the diagonal 
is anextremal diagonal (i.e., the interior of lies in the exterior of ).
References
Toussaint, G. ``Anthropomorphic Polygons.'' Amer. Math. Monthly 122, 31-35, 1991.
- Parallelogram
- Parallelogram Illusion
- Parallelogram Law
- Parallelohedron
- Parallelotope
- Parallel Postulate
- Parallel (Surface of Revolution)
- Paralogic Triangles
- Parameter
- Parameterization
- Parameter (Quadric)
- Parametric Latitude
- Parametric Test
- Pareto Distribution
- Parity
- Parity Constant
- Parking Constant
- Parodi's Theorem
- Parry Circle
- Parry Point
- Parseval's Integral
- Parseval's Relation
- Parseval's Theorem
- Partial Derivative
- Partial Differential Equation