| S/N | Signal to noise ratio |
| SAM | Service Access Multiplexer |
| SAN | Storage-Area Network |
| SAP | Service Access Point |
| SAR | Synthetic Aperture Radar |
| SAR | Successive Approximation Register |
| SAR | Segmentation and Reassembly |
| SAR | Specific Absorption Rate |
| SARA | Short Range Automotive Radar Frequency Allocation |
| SAW | Surface Acoustic Wave |
| S-Band | Short Band |
| SBS | Stimulated Brillouin Scattering |
| SCADA | Supervisory Control and Data Acquisition |
| Scan | Switched-Circuit Automatic Network |
| SCCP | Signaling Connection Control Part |
| SCCS | Switching Control Center System |
| SCE | Service-Creation Environment |
| SCF | Service Control Function |
| SCL | Service Control Language |
| SCM | Service Combination Manager OR Station Class Mark OR Subscriber Carrier Mark |
| SCN | Service Circuit Node OR Switched-Circuit Network |
| SCP | Service Control Point |
| SCR | Sustainable Cell Rate |
| SCRAM | Static Radom Access Memory |
| SCSP | Server Cache Synchronization Protocol |
| SCTP | Simple Computer Telephony Protocol OR Simple Control Transport Protocol OR Stream control Transmission Protocol |
| SD | Selective Discard |
| SD&O | Service Development and Operations |
| SDA | Separate Data Affiliate |
| SDB | Service Design Bureau |
| SDC | Service Design Center |
| SDF | Service Data Function |
| SDH | Synchronous Digital Hierarchy |
| SDL | System Definition Language |
| SDM | Service-Delivery Management OR Shared Data Model |
| SDMA | Space Division Multiple Access |
| SDN | Software-Defined Network |
| SDO | Standards Developing Organization |
| SDP | Session Description Protocol |
| SDR | Software Defined Radio |
| SDRAM | Synchronous Dynamic RAM |
| SDRAM/SORAM | Synchronous Dynamic Random Access Memory |
| SDRP | Source Demand Routing Protocol |
| SDSL | Symmetric DSL |
| SDTV | Synchronous Digital Hierarchy |
| SDU | Service Data Units |
| SDV | Switched Digital Video |
| SE | Service Element |
| SEAMCAT | Spectrum Engineering Advanced Monte Carlo (computer) Analysis Tool (software implementation of a Monte Carlo simulation method which permits statistical modeling of different radio interference situations) |
| SEC | Securities and Exchange Commission |
| SECOM | Secure Communications |
| SEE | Service-Execution Environment |
| SEM | Spectral Emission Mask |
| SEP | Signaling Endpoint |
| ServReq | Service Request |
| SET | Secure Electronic Transaction |
| SEU | Single-Event Upset |
| SFA | Sales Force Automation |
| SFD | Start Frame Delimiter |
| SFDR | Spurious Free Dynamic Range |
| SFF | Small Form-Factor |
| SFGF | Supplier-Funded Generic Element |
| SFM | Single Frequency Network |
| SFQ | Single Flux Quantum |
| SG | Signaling Gateway |
| SG&A | Selling, Goods, and Administration OR Sales, Goods, and Administration |
| SGCP | Simple Gateway Control Protocol |
| SGSN | Service GPRS Support Node |
| SHLR | Standalone Home Location Register |
| SHV | Shareholder Value |
| SI | Service Information OR Systems Integrator |
| SIBB | Service-Independent Building Block |
| SiC | Silicon-Carbide |
| SIC | Service Initiation Charge |
| SICL | Standard Interface Control Library |
| SID | Silence Indicator Description |
| SIDS | Shoreline Intruder Detection System |
| SIF | SONET Interoperability Forum |
| SIG | Specification Implementation Group |
| SiGe | Silicon Germanium |
| SIGe:C | Silicon Germanium:Carbon |
| sigtran | Signaling Transport [working group] |
| SIM | Subscriber Identity Module OR Service Interaction Manager |
| SINAD | Signal to toal noise and Interference ratio |
| SiP | System-in-a-Package |
| SIP | Session Initiation Protocol |
| SIP CPL | SIP Call Processing Language |
| SIP-T | Session Initiation Protocol for Telephony |
| SIR | Serial Infrared |
| SITA | Societe Internationale de Telecommunications Aeronautiques |
| SIU | Service Interface Unit |
| SIVR | Speaker-Independent Voice Recognition |
| SKU | Stock-Keeping Unit |
| SL | Service Logic |
| SLA | Service-Level Agreement |
| SLC | Subscriber Line Carrier |
| SLC | Single Layer Capacitors |
| SLEE | Service Logic Execution Environment |
| SLIC | Subscriber Line Interface Circuit |
| SLO | Service-Level Objective |
| SM | Sparse Mode |
| SMC | Service Management Center |
| SMD | Short Message Delivery |
| SMDI | Simplified Message Desk Interface |
| SMDS | Switched Multimegabit Data Service |
| SME | Superconducting Microelectronics |
| SME | Small-Top-Medium Enterprise |
| SMF | Single-Mode Fiber |
| SML | Service Management Layer |
| SMP | Service Management Point |
| SMPP | Short Message Peer-To-Peer Protocol |
| SMPS | Switched Mode Power Supplies |
| SMR | Specialized Mobile Radio |
| SMS | Short Messaging Service OR Service-Management System |
| SMSC | Short Messaging Service Center |
| SMT | Surface-Mount Technology or Surface-Mount Toroidal |
| SMTP | Simple Mail Transfer Protocol |
| SN | Service Node |
| SNA | Service Node Architecture |
| SNA | Service Network Architecture |
| SNAP | Subnetwork Access Protocol |
| SNMP | Simple Network Management Protocol |
| SNPP | Simple Network Paging Protocol |
| SNR | Signal-to-Noise Ratio |
| SO | Service Objective |
| SOA | Semiconductor Optical Amplifier OR Service Order Activation |
| SOAC | Service Order Analysis and Control |
| SOAP | Simple Object Access Protocol |
| SoC | System-on-Chip |
| SOCC | Satellite Operations Control Center |
| SOE | Standard Operating Environment |
| SOFDMA | Scalable Orthogonal Frequency Division Multiplexing Access |
| SOHO | Small Office, Home Office |
| SOI | Silicon On Insulator |
| SOIC | Small-Outline Integrated Circuit |
| SON | Service Order Number |
| SONET | Synchronous Optical Network |
| SOP | Service Order Processor |
| SOT | Standard Outline Transistor package |
| SoTDMA | Self organizing TDMA |
| SOWS | Side Obstacle Warning Systems |
| SP | Service Provider OR Signaling Point |
| S-parameter | Scattering Parameter |
| SPC | Stored Program Control |
| SPDT | Single-Pole Double-Throw |
| SPE | Synchronous Payload Envelope |
| SPF | Shortest Path First |
| SPI | Serical Peripheral Interface |
| SPICE | Stimulation Program with Integrated Circuit Emphasis |
| Spirits | Service In The PSTN/IN Requesting Internet Service [working group] |
| SpiritsG | SPIRITS Gateway |
| SPM | Self-Phase Modulation OR Subscriber Private Meter |
| SPOP | Service Point of Presence |
| SPR | Sector Power Ratio |
| SPVC | Security Policy Verification Committee |
| SPX | Sequence Packet Exchange |
| SQL | Structured Query Language |
| SRAM | Static Random Access Memory |
| SRD | Short Range Device |
| SRF | Special Resource Function |
| SRP | Source Routing Protocol |
| SRR | Short Range Radar |
| SRS | Stimulated Raman Scattering |
| srTCM | Single-Rate Tri-Color Marker |
| SS | Softswitch |
| SS7 | Signaling System 7 |
| SSE | Service Subscriber Element |
| SSF | Service Switching Function |
| SSG | Service Selection Gateway |
| SSL | Secure Sockets Layer |
| SSM | Service and Sales Management |
| SSMF | Standard Single-Mode Fiber |
| SSN | Starting Sequence Number |
| SSOP | Plastic Shrink Small Outline Package |
| SSP | Service Switching Point |
| SSPA | Solid State Power Amplifiers |
| STC | Space/Time Coding |
| STE | Section Terminating Equipment |
| STI | Service Transport Interface |
| STM | Synchronous Transfer Mode |
| STN | Service Transport Network Or Service Transport Node |
| STP | Shielded Twisted Pair OR Signal Transfer Point OR Spanning Treee Protocol |
| STR | Signal-To-Resource |
| STS | Synchronous Transport Signal |
| SUA | SCCP User Adaptation |
| SVC | Switched Virtual Circuit |
| SW | Software |
| SWAN | Storage Wide-Area Network |
| SWAP | Shared Wireless Access Protocol |
| SWBT | Southwestern Bell Telephone |
| SWOT | Strengths, Weaknesses, Opportunities, and Threats |
| SYN | IN Synchronous Transmission |
| sysRAM | System RAM |