Griffiths' Theorem
When a point 
moves along a line through the Circumcenter of a given Triangle 
, the Circumcircle of the Pedal Triangle of with respect to passes through a fixed point (the Griffiths Point) on the Nine-Point Circle of .
- Witness
- Wittenbauer's Parallelogram
- Wittenbauer's Theorem
- Witten's Equations
- Wolstenholme's Theorem
- Woodall Number
- Woodbury Formula
- Word
- World Line
- Worm
- Worpitzky's Identity
- Writhe
- Wronskian
- Wulff Shape
- Wynn's Epsilon Method
- Wythoff Array
- Wythoff Construction
- Wythoff's Game
- Wythoff Symbol
- x-Axis
- Xi Function
- x-Intercept
- XOR
- Yacht
- Yanghui Triangle