| R | Resistor; Rosin (flux) |
| R | Potentiometer |
| R | Resistance |
| R&D | Research and Development |
| RA | Rosin Activated |
| RAC | Remote Access and Control; Rambus ASIC Cell |
| RADAR | RAdio Direction And Ranging |
| RAE | Residue After Evaporation |
| RAID | Redundant Arrays of Inexpensive Disks |
| RAIRS | Reflection-Absorption InfraRed Spectroscopy |
| RAM | Random Access Memory |
| RAM | Reliability, Availability, and Maintainability |
| RAMP | Reliability Analysis and Modeling Program |
| RAS | Sun Raster Image format |
| RAW | Raw file image format |
| RBB | Base sheet resistance |
| RBOC | Regional Bell Operation Company |
| RBS | Resonant Bond Scattering; Rutherford Backscattering Spectrometry; Refractive backscattering |
| RBSOA | Reverse Bias Safe Operating Area |
| RBW | Resolution BandWidth |
| RC | Resistance-capacitance, also Radio controlled |
| RCCL | Return Channel Cable and LMDS DTV platforms |
| RCS | Revision Control System; Return Channel Satellite; Radar Cross-Section |
| RCT | Reference Cluster Tool; Return Channel Terrestrial |
| RCTT | DVB-RCT Terminal |
| RDF | Resource Description Framework |
| RDR | Rotating Disk Reactor |
| RDRAM | Rambus Dynamic Random Access Memory |
| RDS | Radio data system |
| RDT | Real Data Transport |
| RE | Rare Earths |
| REL | Recommended Exposure Limit; Rights Expression Language |
| REM | Reflection Electron Microscopy |
| RETMA | Radio Electronics TV Manufacturers Assoc |
| RF | Radio Frequency |
| RF | Resonance Frequency |
| RfC | Request for Comment |
| RFI | Radio frequency interference |
| RFI | Request For Information |
| RFIC | Radio Frequency Integrated Circuit |
| RFICP | Radio Frequency ICP |
| RFID | Radio Frequency IDentification |
| RFM | Radio frequency monitoring |
| RFO | Restricted flow orifice |
| RFP | Radio Frequency Probe |
| RfP | Request for Plan; Request for Proposal |
| RFQ | Request for quote |
| RFS | Regardless of Feature Size |
| RFT | Resistive Force Theory |
| RGA | Residual gas analysis |
| RH | Relative humidity |
| RHCP | Right Hand Circularly Polarized |
| RHEED | Reflection High-Energy Electron Diffraction |
| RHET | Resonant Hot-tunnelling Electron Transistor |
| RIBE | Reaction Ion Beam Etching |
| RIE | Reactive Ion Etching |
| RIM | Read-in mode |
| RIP | Raster Image Processor |
| RISC | Reduced Instruction Set Computer/Computing |
| RIST | Rule induction and statistical testing |
| RKE | Remote Keyless Entry system |
| RL | Load resistor |
| RL | Return Loss |
| RLC | Resistance-capacitance-inductance |
| RLE | Windows or CompuServe RLE image format |
| RLI | Resist LIthography |
| RMA | Rosin Mildly Activated |
| RMI | Remote Method Invocation |
| RMOS | Refractory Metal-Oxide Semiconductor |
| RMS | Recipe Management Standard |
| RMS | Root mean square |
| RMSEP | Root Mean Square Error of Prediction |
| RMTF | Recipe Management Task Force |
| RN | Noise Resistance |
| RNN | Recurrent Neural Network |
| RO | Reverse Osmosis |
| ROC | Remote Object Communications |
| ROE | Return On Equity |
| ROI | Return On Investment |
| ROM | Read Only Memory |
| ROM | Rough Order of Magnitude |
| ROS | Record-On-Silicon |
| ROV | Remote Operated Vehicle |
| ROX | Run Of eXperiments |
| RPC | Remote Procedure Call |
| RPM | Revolutions Per Minute |
| RPM | Rotations Per Minute |
| RPN | Residual Phase Noise |
| RPR | Resilient Packet Ring |
| RQ | Reportable Quantity |
| RR | Removal Rate |
| RRMSEP | Relative Root Mean Square Error of Prediction |
| RSE | Reactive sputter etch |
| RSH | Remote SHell |
| RSM | Response surface methodology; response surface matrix |
| RSS | RDF Site Summary |
| RSSI | Radio Signal Strength Indicator |
| RST | Reynolds Stress |
| RSVP | Resource Reservation Protocol |
| RT | Real Time |
| RT | Room Temperature |
| RTA | Rapid Thermal Anneal |
| RTB | Real-time backplane |
| RTCP | Real-Time Control Protocol |
| RTCVD | Rapid thermal chemical vapor deposition |
| RTD | Resistance Temperature Detector; Resonant Tunneling Diode |
| RTF | Rich Text Format |
| RTL | Resistor-transistor logic; register transfer level |
| RTM | Rapid thermal multiprocessing |
| RTO | Rapid thermal oxidation; Regenerative thermal oxidizer |
| RTO | S Real Time Operating System |
| RTP | Rapid Thermal Processing; Real-Time Transport Protocol |
| RTR | Real-time reporting |
| RTS | Request to send; Random Telegraph Signal |
| RTSP | Real-Time Streaming Protocol |
| RTSPC | Real-Time Statistical Process Control |
| RTV | Room Temperature Vulcanizing |
| RTY | ReTrY limit |
| RZ | Return to Zero |
| Ra | Radium |
| Rad | Radian |
| rcvr | Receiver |
| rect | Rectifier |
| ref | Reference |
| Ref | Reference Voltage |
| rf | Radio frequencies |
| RL | Load resistor |
| RS232 | Norm for serial transmission |
