Computing

• SL (complexity), a class of computational complexity
• .sl, the country code top-level domain for Sierra Leone
• Second Life, a massively multi-user 3D virtual world
• Scientific Linux, a Linux distribution

Transport

• Mercedes-Benz SL, an automobile
• Rio Sul Serviços Aéreos Regionais, IATA code SL, a Brazilian airline
• Salt Lake City Southern Railroad's reporting mark
• Stor-Oslo Lokaltrafikk, public transport operator in Akershus, Norway
• Storstockholms Lokaltrafik, public transport operator in Stockholm, Sweden

Organisations

• Sendero Luminoso, the "Shining Path" Maoist guerrilla movement
• SL Corporation, a Korean auto parts company
• Stronnictwo Ludowe, a defunct Polish party

Other uses

• Sl, the abbreviation for the orchid genus Sophrolaelia
• sl, Slovene language ISO 639-1 code
• s.l., sine loco, used in bibliographies to indicate that the place of publication of a document is unknown
• s.l., sensu lato, used in taxonomy to mean "in the wider sense" of a definition
• SL_n, Special linear group in mathematics
• sl, special linear Lie algebra in mathematics
• Serjeant-at-law, an obsolete legal position in the United Kingdom
• Standard Level, a level of course difficulty in the International Baccalaureate Diploma Programme
• Seditious Libeler, the initials SL were branded onto the faces of certain Protestants by Archbishop William Laud