| S.O. | Signed Only 
| Others |
| S/O | Section Officer
| Others |
| S/O | Security Officer
| Others |
| S/O | Seller's Option
| Others |
| S/O | Shipowner
| Others |
| S/O | Shipping Order
| Others |
| S/O | Shout Out
| Others |
| S/O | Shout-Out
| Others |
| S/O | Shutoff
| Others |
| S/O | Significant Other
| Others |
| S/O | Sold Out
| Others |
| S/O | Sold-Out
| Others |
| S/o | Son of
| Others |
| S/O | Switchover
| Others |
| SO | Safety Observer
| Others |
| SO | Safety Officer
| Others |
| SO | Sales Order
| Others |
| SO | Salpingo-Oophorectomy
| Others |
| SO | Sarts Oscar
| Others |
| SO | Satellite Office
| Others |
| SO | Scene Object
| Others |
| SO | Seated Only
| Others |
| SO | Second Opinion
| Others |
| SO | Second Order
| Others |
| SO | Secondary Oocyte
| Others |
| SO | Section Officers
| Others |
| SO | Self Organizing
| Others |
| SO | Senior Officer
| Others |
| SO | Senior Opinion
| Others |
| SO | Serving Office
| Others |
| SO | Sex Offender
| Others |
| so | Shared Object
| Others |
| SO | Shared object (Fortran 90)
| Others |
| SO | Shared Objects
| Others |
| SO | Sheriff's Office
| Others |
| SO | Shift Out
| Others |
| SO | Shoot Out
| Others |
| SO | Shop Order
| Others |
| SO | Shoulder Orthosis
| Others |
| SO | Show Off
| Others |
| SO | Side Of
| Others |
| SO | Sign Off
| Others |
| SO | Sign Out
| Others |
| SO | Silent Observer
| Others |
| SO | Silesie Orientale
| Others |
| SO | sine oculis (gene)
| Others |
| SO | Single Output
| Others |
| SO | Sistema Operativo
| Others |
| SO | Sleep Onset
| Others |
| SO | Slip On
| Others |
| SO | Sloganeering Org
| Others |
| SO | Small Outline
| Others |
| SO | Small Outline (package)
| Others |
| SO | SO in our
| Others |
| SO | Soap Opera
| Others |
| SO | Soletta
| Others |
| SO | Solitron
| Others |
| SO | Somali
| Others |
| SO | Somalia
| Others |
| SO | Some Of ....
| Others |
| SO | Sondrio (Provence)
| Others |
| SO | SOnntag
| Others |
| SO | Sophie Or
| Others |
| SO | Sort Of
| Others |
| SO | Source Out
| Others |
| SO | South Orient
| Others |
| SO | Southampton postcode area
| Others |
| SO | Southern Company
| Others |
| SO | Special Offer
| Others |
| SO | Special officer
| Others |
| SO | Special Operation
| Others |
| SO | Special Operations
| Others |
| SO | Special Order
| Others |
| SO | Special Orders
| Others |
| SO | sphincter of Oddi
| Others |
| SO | Spin Orbit
| Others |
| SO | Stack Overflow
| Others |
| SO | stand for on
| Others |
| SO | Standing Order (Parliamentary procedure)
| Others |
| SO | Standing Orders
| Others |
| SO | Station Officer
| Others |
| SO | Station Offset
| Others |
| SO | Station Operator
| Others |
| SO | Stem Only harvest
| Others |
| SO | Step Off Ministry
| Others |
| SO | Stock Option
| Others |
| SO | Straight On
| Others |
| SO | Strategic Objective
| Others |
| SO | Strategies and Operations
| Others |
| SO | Stream Output
| Others |
| SO | Strike Out
| Others |
| SO | String Orchestra
| Others |
| SO | Structured Obligation
| Others |
| SO | Struvite Oxalate
| Others |
| SO | Student Organizations
| Others |
| SO | Student Orientation
| Others |
| SO | Stykovochnyy Otsek
| Others |
| SO | Sub Office
| Others |
| SO | Substitutive Outlier
| Others |
| SO | suggestive of
| Others |
| SO | Sulfur monoxide
| Others |
| SO | sulphur monoxide
| Others |
| SO | Super Overclock
| Others |
| SO | Superior Oblique
| Others |
| SO | Superior Olive
| Others |
| SO | superoxide
| Others |
| SO | Superseded or Obsolete
| Others |
| SO | Support Operations
| Others |
| SO | Supporting Organization
| Others |
| SO | Supraorbital
| Others |
| SO | Sustainable Operations
| Others |
| SO | Sutures Out
| Others |
| SO | Symptom object
| Others |
| SO | System Operator
| Others |
| SO | System Output
| Others |
| SO | Systolic Output
| Others |
| SO | The Source Of ....
| Others |