- r-vector
- Rydberg, J.R.
- Ryser formula
- Ryser, H.J.
- Réaumur, R.A.F.de
- Rényi, A.
- Rényi entropy
- Rényi parking constant
- Rényi polynomial
- Rényi test
- Rényi theorem
- Rückert, W.
- Rückert zero-point theorem
- Saaty, T.L.
- sabermetrics
- Saccheri, G.
- Saccheri quadrangle
- Sacrobosco, J.de
- s-additive sequence
- saddle
- saddle at infinity
- saddle connection
- saddle-focus
- saddle function
- saddle-like surface