- Schwarzian Derivative
- Shtuka (finite fields theory)
- Skein Modules (knot theory)
- Stable Commutator Lenght (geometric group theory)
- Stack (sheaf theory)
- Swindle (Infinite Swindle, 4-variedades)
- Systole (geometry)
- Syzygy (finitely generated R-module M, where R is a commutative ring)