I (disambiguation)

I is the ninth letter of the alphabet. It can also refer to:

• I (pronoun), the first-person singular pronoun

In astronomy:

• i, the symbol for orbital inclination
• I, in the Yerkes spectral classification scheme the symbol for supergiants

In chemistry:

• I, the symbol for iodine on the periodic table
• I, the symbol for isoleucine in biochemistry

In economics:

• i, the symbol for the interest rate
• I, the symbol for investment

In genetics:

• Haplogroup I (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup
• Haplogroup I (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup

In mathematics:

• 1 (number) in Roman numerals
• i, the imaginary unit for which i² = -1
• I (or I_n), an identity matrix of indeterminate size (or of size n)
• i, an index variable in a matrix
• I_x(a,b), the regularized incomplete beta function (of a variable x and parameters a,b)
• I, the closed unit interval which contains all real numbers from 0 to 1 inclusive
• <math>{\hat{\imath}}</math> (pronounced "i-hat"), the unit vector along the x-axis in Cartesian coordinates

In music:

• I, a diatonic function in tonal music theory
• I (album), the debut album of Kurt Nilsen
• I (band), a band formed by members of Immortal, Enslaved, Gorgoroth, and Sahg
• I (Cilvaringz album), the debut album of Wu-Tang Clan affiliate producer Cilvaringz
• I (EP), an EP by Meshuggah
• I (Magnetic Fields album), an album by the Magnetic Fields
• I, a song on Dehumanizer, an album by Black Sabbath

In physics:

• I and i, symbols for electric current signals in electronic engineering
• I, the moment of inertia

In computer programming:

• i, a common generic index variable often used for looping constructs
• <i>, an HTML element for marking italic type
• .i, the common filename extension for a file that contains the output from a preprocessor.

In radio and television:

• i (TV network), the former name of ION Television
• I band, 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
• I, in the YIQ colorspace commonly used with the NTSC television encoding scheme, the color-difference channel which is in-phase with the subcarrier

Other uses:

• I (kana), one of the Japanese kana that each respresent one mora
• I, the symbol for Italy in the list of international license plate codes
• /i/, /ɨ/ and /ɪ/, in the International Phonetic Alphabet, the three forms of the letter I
• Mitsubishi i, a Japanese kei car
• I, a character in Adventure into Fear who acted as a guide for Morbius, the Living Vampire
• Lowercase i prefix, a common prefix used by Internet and electronic companies