Near-Pencil
An arrangement of 
points such that 
of them are Collinear.
References
Guy, R. K. ``Unsolved Problems Come of Age.'' Amer. Math. Monthly 96, 903-909, 1989.
- Wavelet Matrix
- Wavelet Transform
- Wave Operator
- Wave Surface
- Weak Convergence
- Weak Law of Large Numbers
- Weakly Binary Tree
- Weakly Complete Sequence
- Weakly Independent
- Weakly Triple-Free Set
- Weber Differential Equations
- Weber Functions
- Weber's Discontinuous Integrals
- Weber's Formula
- Weber-Sonine Formula
- Weber's Theorem
- Web Graph
- Wedderburn's Theorem
- Weddle's Rule
- Wedge
- Wedge Product
- Weekday
- Weibull Distribution
- Weierstrass M-Test
- Weierstraß Approximation Theorem