• Secured LAN segment
• MPEG-4 SLS, a scalable to lossless audio standard published by ISO
• Same language subtitle, a technique used to promote literacy through the use of subtitles
• Selective laser sintering a rapid prototyping process
• Swiss Light Source, the Swiss synchrotron
• Serviceability limit State, a factor in limit state design
• Service level specification, a technical interpretation of service level agreements
• Signaling Link Selection or Signalling Link Selection, routing label and field of the MTP2 frame in MTP
• Single-level store, memory management technology of Multics and IBM System i (AS/400)
• Slovenska ljudska stranka, Slovenian for the Slovene People's Party
• Sodium lauryl sulfate
• Softlanding Linux System, one of the first comprehensive Linux distributions
• StarLight Scopes, image intensifier tubes used for night-vision
• Stephenson Locomotive Society
• SLS, initials of the authors of a controversial paper "Nuclear power the energy balance" by Jan Willem Storm van Leeuwen and Philip Smith
• Sim Lim Square, a popular shopping centre for computer hardware in Singapore.
• Surf lifesaving
• SmartLogic Solutions, LLC, a software & consulting firm in Baltimore, MD

In science:

• Swiss Light Source, a Swiss synchrotron at PSI, Villigen, Switzerland.

In education:

• St. Louis School, Hong Kong, a Catholic primary and secondary school
• St. Luke's School, a JK-8 independent school in New York City
• Shawnigan Lake School, a private secondary school
• Stanford University Law School
• Summer Leadership School for Air Force JROTC.

In music:

• Second Life Syndrome a 2005 album by Polish progressive metal band Riverside.
• Speech Level Singing - a singing technique