Windmill
One name for the figure used by Euclid 
to prove the Pythagorean Theorem.
- Cliff Random Number Generator
- Clique
- Clique Number
- Clock Solitaire
- Closed Curve
- Closed Curve Problem
- Closed Disk
- Closed Form
- Closed Graph Theorem
- Closed Interval
- Closed Set
- Close Packing
- Closure
- Clothoid
- Clove Hitch
- Clump
- Cluster
- Cluster Perimeter
- C-Matrix
- Coanalytic Set
- Coastline Paradox
- Coates-Wiles Theorem
- Coaxal Circles
- Coaxaloid System
- Coaxal System