Look up I, i, i-, or -i in Wiktionary, the free dictionary.

I is the ninth letter of the Latin alphabet.

I or i may also refer to:

Language

• I (pronoun), the first-person singular subject pronoun in English
• I (Cyrillic), a letter used in almost all ancient and modern Cyrillic alphabets
• ı, dotless I, letter used in Turkish and Azerbaijani
• i, close front unrounded vowel, in the International Phonetic Alphabet
• ɨ, close central unrounded vowel, in the International Phonetic Alphabet
• ɪ, near-close near-front unrounded vowel, in the International Phonetic Alphabet
• I (kana), one of the Japanese kana that each represent one mora
• I, male prefix to some Balinese names

Science, technology, and mathematics

Biology

• Troponin I, one of the three troponins
• Haplogroup I (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
• Haplogroup I (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup
• Olfactory nerve, the 1st cranial nerve in human anatomy
• the Lợn Ỉ or Vietnamese Pot-bellied pig

Chemistry

• Iodine, symbol I, a chemical element
• I, isoleucine, an amino acid
• I, ionic strength in a chemical solution
• i, Van 't Hoff factor

Computing

• i, a common generic index variable often used in program loops
• <i>, an HTML element for marking italic type
• .i, the common filename extension for a file that contains the output from a preprocessor
• i-, a prefix for Apple products e.g. iMac, iPod, iPhone
• i-, an Internet-related prefix used by Internet and electronic companies

Mathematics

• I, the Roman numeral for 1
• i, imaginary unit, for which i² = −1
• I or I_n, identity matrix of indeterminate size (or of size n)
• I, unit interval, which contains all real numbers from 0 to 1 inclusive
• i, an index variable, e. g. in a matrix or for summation
• I_x(a,b), the regularized incomplete beta function (of a variable x and parameters a,b)
• î, the unit vector along the x-axis in Cartesian coordinates

Physics and astronomy

• I, i, electric current
• I, isospin
• I, luminous intensity
• I, moment of inertia
• i, orbital inclination
• I (Roman number one), in the Yerkes spectral classification scheme, the symbol for supergiants

Telecommunication

• I band (NATO), the range of radio frequencies from 8 GHz to 10 GHz in the electromagnetic spectrum
• I, the ITU prefix allocated to Italy in radio communication
• I, in QAM modulation schemes, the in-phase communications channel

Other uses in technology

• i, a suffix unit for video resolution (vertical Interlaced lines), as in 480i or 1080i
• I, in the YIQ colorspace commonly used with the NTSC television encoding scheme, the color-difference channel which is in-phase with the subcarrier

Arts and media

Music

• I (band), a Norwegian heavy metal band
• I, a diatonic function in tonal music theory

Albums

• i (A.R. Kane album), 1989
• I (Ben Lester album), 2019
• I (Cilvaringz album), 2007
• I (Cursed album), 2003
• I (Die Krupps album), 1992
• I (Felix Jaehn album), 2018
• I (Ikimono-gakari album), 2013
• I (Imminence album), 2014
• I (Jaejoong EP), 2013
• I (JonnyX and the Groadies album), 2005
• I (Juju album), 2018
• I (Kingston Wall album), 1992
• I (Kurt Nilsen album), 2003
• i (The Magnetic Fields album), 2004
• I (Meshuggah EP), 2004
• i (Misako Odani album), 1997
• I (Nightingale album), 2000
• I (Sahg album), 2006
• I (Taeyeon EP), 2015
• I (Xerath album), 2009
• I (soundtrack), by A. R. Rahman from the eponymous 2015 film

Songs

• "i" (Kendrick Lamar song), a 2014 song by Kendrick Lamar from his album To Pimp a Butterfly
• "i" (Lil Skies song), a song 2019 by Lil Skies from his debut album Shelby
• "I" (Taproot song), a 2001 song by band Taproot from their album Gift
• "I (Who Have Nothing)", a 1966 Ben. E. King song also recorded by Tom Jones, who used the title for one of his albums
• "I", a 2003 song on Weather Systems, an album by Andrew Bird
• "I", a 1992 song on Selected Ambient Works 85–92, an album by Aphex Twin
• "I", a 1992 song on Dehumanizer, an album by Black Sabbath
• "I", a 1997 song on Coal Chamber, an album by Coal Chamber
• "I", a 1967 song on Underground, an album by The Electric Prunes
• "I", a 2012 song on Muse, an album by Jolin Tsai
• "I", a 1981 song on Music from "The Elder", an album by Kiss
• "I", a 1994 song on Made in USA, an album by Pizzicato Five
• "I", a 1999 song on Eternal, an album by Samael
• "I", a 2003 song on Winter Story, an album by Shinhwa
• "I", a 2008 song on In the Shadow of a Thousand Suns, an album by Abigail Williams
• "I", a 2011 song on Cinderella's Eyes, an album by Nicola Roberts
• "I", a 2015 song on I, an EP by Taeyeon
• "I", a 2016 song by Rezz
• "I", a 2019 song by Hey! Say! JUMP

Other media

• I (2015 film), an Indian Tamil-language film
• I (2016 film), an Iranian film
• i (TV network), the former name of ION Television
• i (newspaper), a British newspaper based in London
• i (Portuguese newspaper), a Portuguese newspaper based in Lisbon
• I, a character in the comic book series Adventure into Fear
• "I" Is for Innocent, the ninth novel in Sue Grafton's "Alphabet mystery" series, published in 1992
• I, a Man, a 1967 Andy Warhol film

Mythology

• Goddess I, a Mayan deity
• Hou-i, or I, a heroic archer and hunter in Chinese mythology

Vehicles and transportation

• Italy (I), in the list of international vehicle registration codes
• Italy (aircraft registration prefix)
• Mitsubishi i, a Japanese kei car
• I (Los Angeles Railway), a former streetcar line in Los Angeles
• Toei Mita Line, a subway service operated by the Tokyo Metropolitan Bureau of Transportation (Toei), labeled
• Imazatosuji Line, a subway service operated by the Osaka Metro, labeled
• , the official West Japan Railway Company service symbol for the Kakogawa Line.

Other uses

• i, an international symbol for visitor or tourist information; see ISO 7001
• Nintendo DSi, the third model in the Nintendo DS line, released in 2008
• Nintendo DSi XL, the larger version of the DSi, released in 2009
• I, an alternative romanization of Lee (Korean surname)
• I-Foundation, a charity in charge of state-funded Hindu faith schools in the United Kingdom
• Interest rate (i), in economics
• Investment (I), in economics
• India, the military time zone code for UTC+09:00