KSI (born 1993; Olajide Olatunji) is an English YouTube personality, musician and professional boxer.

Look up ksi or KSI in Wiktionary, the free dictionary.

KSI or Ksi may also refer to:

• Killed or Seriously Injured, in road safety
• Kontoret för särskild inhämtning ("Office for Special Collection"), a Swedish intelligence agency
• The Korean Studies Institute, a research institution on Korean studies in South Korea
• KSI Industries, a fictional company in Transformers: Age of Extinction
• KSI, IATA code for Kissidougou Airport in Guinea
• Icelandic: Knattspyrnusamband Íslands (Football Association of Iceland), Icelandic sports group
• ksi (unit), kilopound per square inch, a non-SI unit of stress or pressure
• Ksi (Cyrillic), a letter of the early Cyrillic alphabet (Ѯ, ѯ) derived from the Greek letter Xi

• The Greek letter Ξ/ξ, pronounced [ksi] in Greek

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