Pedal Line
Mark a point 
on a side of a Triangle and draw the perpendiculars from the point to the two other sides. The linebetween the feet of these two perpendiculars is called the pedal line.
- Connected Sum
- Connected Sum Decomposition
- Connection
- Connection Coefficient
- Connectivity
- Connes Function
- Conocuneus of Wallis
- Conoid
- Consecutive Number Sequences
- Conservation of Number Principle
- Conservative Field
- Consistency
- Consistency Strength
- Constant
- Constant Function
- Constant Precession Curve
- Constant Problem
- Constant Width Curve
- Constructible Number
- Constructible Polygon
- Construction
- Constructive Dilemma
- Contact Angle
- Contact Number
- Contact Triangle