Rodrigues's Curvature Formula
where
is the unit Normal Vector and 
is one of the two Principal Curvatures.See also Normal Vector, Principal Curvatures- Stochastic Calculus of Variations
- Stochastic Group
- Stochastic Matrix
- Stochastic Process
- Stochastic Resonance
- Stokes Phenomenon
- Stokes' Theorem
- Stolarsky Array
- Stolarsky-Harborth Constant
- Stolarsky's Inequality
- Stomachion
- Stone Space
- Stone-von Neumann Theorem
- Stopper Knot
- Straight Angle
- Straightedge
- Straight Line
- Straight Polyomino
- Strange Attractor
- Strange Loop
- Strangers
- Strassen Formulas
- Strassman's Theorem
- Strassnitzky's Formula
- Strategy