China 
Africa 
- Red beds
- Red blood cell
- Red blood cell distribution width
- Red cell distribution width
- Red color
- Red edge
- Red lead
- Red light cameras
- Red meat
- Red mud
- Red nucleus
- Red pulp
- Red tide
- Red-hardness
- Redacted
- Redfield ratio
- Redirection
- Redis
- Redistribution
- Redistribution layer
- Redox
- Redox gradient
- Redox indicator
- Redox titration
- Redoximorphic features
- Redshift
- Reduced cost
- Reduced derivative
- Reduced form
- Reduced level
- Reduced mass
- Reduced product
- Reduced properties
- Reduced row echelon form
- Reduced temperature
- Reducing agents
- Reducing atmosphere
- Reductase
- Reduction of order
- Reductive amination
- Reductive dechlorination
- Reductive elimination
- Redundancy
- Reeb graph
- Reed relay
- Reed switch
- Reefs
- Reel-to-reel
- Reeler
- Reelin
- Reentrancy
- Reentry
- Refactoring
- Reference architecture
- Reference beam
- Reference class forecasting
- Reference data
- Reference doses
- Reference electrode
- Reference ellipsoid
- Reference frames
- Reference genome
- Reference model
- Reference noise
- Reference plane
- Reference ranges
- Reference standards
- References
- Referential integrity
- Referrals
- Referred pain
- Refinement
- Refineries
- Refinery
- Refining
- Reflectance
- Reflection
- Reflection coefficient
- Reflection seismology
- Reflection symmetry
- Reflections
- Reflective crack
- Reflective equilibrium
- Reflective surfaces
- Reflectometry
- Reflector
- Reflectron
- Reflex arcs
- Reflex klystron
- Reflexes
- Reflexive
- Reflexive relation
- Reflexive space
- Reflow soldering
- Reflux
- Reforestation
- Refraction
- Refractive index
- Refractive index detector
- Refractive index profile
- Refractive surgery
- Refractometer
- Refractory
- Refractory metals
- Refractory period
- Refresh
- Refresh rate
- Refreshable braille display
- Refrigerants
- Refrigeration
- Refrigeration cycle
- Refrigerator
- Refuges
- Refugia
- Refurbishment
- Refuse collection
- Regasification
- Regelation
- Regeneration
- Regenerative braking
- Regenerative cooling
- Regenerative design
- Regenerative fuel cell
- Regenerative heat exchanger
- Regenerative medicine
- Regenerator
- Regenerators
- Region growing
- Regional integration
- Regionalized variable theory
- Regioselectivity
- Registers
- Regolith
- Regression
- Regression analysis
- Regression dilution
- Regression to the mean
- Regression toward the mean
- Regression-kriging
- Regret
- Regula falsi
- Regular
- Regular dodecahedron
- Regular expressions
- Regular graph
- Regular grid
- Regular icosahedron
- Regular languages
- Regular measure
- Regular polygon