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.
- Transcendental Number
- Transcritical Bifurcation
- Transfer Function
- Convergent Sequence
- Convergent Series
- Conversion Period
- Convex
- Convex Function
- Convex Hull
- Convex Optimization Theory
- Convex Polygon
- Convex Polyhedron
- Convolution
- Convolution Theorem
- Conway-Alexander Polynomial
- Conway Groups
- Conway Notation
- Conway Polyhedron Notation
- Conway Polynomial
- Conway Puzzle
- Conway's Constant
- Conway Sequence
- Conway's Game of Life
- Conway's Knot
- Conway's Knot Notation