- Relax NG
- Relaxation
- Relaxation length
- Relaxation oscillator
- Relaxation time
- Relaxin
- Relaxometry
- Relaxor ferroelectrics
- Relay channel
- Relay lenses
- Relay logic
- Relay networks
- Relay valve
- Relays
- Release agents
- Release liner
- Releasing hormone
- Relevance feedback
- Relevance vector machine
- Relevant cost
- Reliability
- Reliability block diagram
- Reliability engineering
- Reliability index
- Reliability prediction for electronic components
- Reliable multicast
- Relicts
- Relief
- Relief ratio
- Relief valves
- Relocated
- Relocation
- Reluctance
- Reluctance motor
- Remainder
- Remanufacturing
- Remdesivir
- Remedial action
- Reminders
- Remineralization
- Reminiscence therapy
- Remission
- Remote assistance
- Remote controls
- Remote data transmission
- Remote diagnostics
- Remote manipulator
- Remote monitoring and control
- Remote patient monitoring
- Remote plasma
- Remote sensing
- Remote surgery
- Remote visual inspection
- Remus
- Remyelination
- Ren
- Renal artery
- Renal artery stenosis
- Renal biopsy
- Renal blood flow
- Renal cell carcinoma
- Renal colic
- Renal corpuscle
- Renal cortex
- Renal glucose reabsorption
- Renal ischemia
- Renal osteodystrophy
- Renal pelvis
- Renal physiology
- Renal threshold
- Renal vein
- Rename
- Rendered
- Rendering
- Rendering equation
- Rendezvous
- Renewable Energy Certificate
- Renewable diesel
- Renewable energy
- Renewable energy certificates
- Renewable fuels
- Renewable heat
- Renewable natural gas
- Renewable resources
- Renewable thermal energy
- Renewal process
- Renewal theory
- Renin
- Renin-angiotensin system
- Rennet
- Renormalization
- Renormalization group
- Renovascular hypertension
- Rent-seeking
- Rep
- RepRap
- Repairability
- Repast
- Repeat unit
- Repeatability
- Repeated game
- Repeated incremental pruning to produce error reduction
- Repeated measures design
- Repeater
- Repeater insertion
- Reperfusion injury
- Repertory grid
- Repetitive control
- Replace
- Replay attacks
- Replica plating
- Replicas
- Replication
- Replication stress
- Replicator equation
- Replisome
- Repointing
- Repolarization
- Reporter gene
- Reporting bias
- Repository
- Repowering
- Representation
- Representation theorem
- Representation theory
- Representations
- Representative elementary volume
- Representative volume element
- Representer theorem
- Repressors
- Reprocessed uranium
- Reproducibility
- Reproductive medicine
- Reproductive success
- Reproductive system
- Reproductive technology
- Reproductive toxicity
- Reprogramming
- Reprojection error
- Reptation
- Reputation systems
- Requirement diagram
- Requirements analysis
- Requirements elicitation
- Requirements engineering
- Requirements management
- Requirements traceability
- Resampling
- Resazurin
- Rescaled range