| Abbreviation | Definition |
|---|---|
| SIS | Short-Interval Scheduler |
| SJ | Svalbard and Jan Mayen Islands |
| SK | SasKatchewan |
| SK | Slovakia (Slovak Republic) |
| SL | Sierra Leone |
| SLP | Slip |
| SM | San Marino |
| SN | Senegal |
| SO | Somalia |
| SOP | Standard Operating Procedure |
| SOP | Standard Operating Procedures |
| SPBS | Small Parcel and Bundle Sorter |
| SPC | Space |
| SPLSM | Single-Position Letter Sorting Machine |
| SPLY | Same Period Last Year |
| SPO | Serving Post Office |
| SPR | Small Parcels and Rolls |
| SR | Suriname |
| SSIS | Schedules and Schemes Information System |
| SSM | Sack Sorting Machine |