- ratio test
- Rauch comparison theorem
- raw score
- ray
- ray bundle
- ray,halfline
- ray ideal class group
- ray ideal class number
- Rayleigh distribution
- Rayleigh quotient iteration method
- Rayleigh-Ritz method
- Rayleigh-Ritz method
- Rayleigh-Ritz method
- Rayleigh scattering
- Rayleigh-Tayler instability
- ray of a congruence
- Razumikhin's condition
- R-chain
- r-closed space
- R-conjugacy
- R-controllability of singular system
- r-dimensional skeleton of simplicial complex
- reachability
- reachability of Petri net
- reachable set of singular system