I, the symbol for investment

/i/, /ɨ/ and /ɪ/, in the International Phonetic Alphabet, the three forms of the letter I

I, the symbol for iodine on the periodic table

i, the symbol for the interest rate

I, in the Yerkes spectral classification scheme the symbol for supergiants

<i>, an HTML element for marking italic type

i, an index variable in a matrix

i (TV network), the former name of ION Television

Mitsubishi i, a Japanese kei car

I and i, symbols for electric current signals in electronic engineering

1 (number) in Roman numerals

I, the moment of inertia

Haplogroup I (Y-DNA), a Y-chromosomal DNA (Y-DNA) haplogroup

I, in QAM modulation schemes, the in-phase communications channel

.i, the common filename extension for a file that contains the output from a preprocessor.

I, the symbol for Italy in the list of international license plate codes

I, a diatonic function in tonal music theory

I, the ITU prefix allocated to Italy in radio communication

i, the imaginary unit for which i² = -1

I, a song on Dehumanizer, an album by Black Sabbath

<math>{\hat{\imath}}</math> (pronounced "i-hat"), the unit vector along the x-axis in Cartesian coordinates

Lowercase i prefix, a common prefix used by Internet and electronic companies

I_x(a,b), the regularized incomplete beta function (of a variable x and parameters a,b)

I, in the YIQ colorspace commonly used with the NTSC television encoding scheme, the color-difference channel which is in-phase with the subcarrier

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

I, the symbol for isoleucine in biochemistry

I (pronoun), the first-person singular pronoun

I, a character in Adventure into Fear who acted as a guide for Morbius, the Living Vampire

I (Cilvaringz album), the debut album of Wu-Tang Clan affiliate producer Cilvaringz

I (or I_n), an identity matrix of indeterminate size (or of size n)

I (kana), one of the Japanese kana that each respresent one mora

I (EP), an EP by Meshuggah

I, the closed unit interval which contains all real numbers from 0 to 1 inclusive

I band, the range of radio frequencies from 8 GHz to 10 GHz in the electromagnetic spectrum

I (Magnetic Fields album), an album by the Magnetic Fields

I (band), a band formed by members of Immortal, Enslaved, Gorgoroth, and Sahg

Haplogroup I (mtDNA), a human mitochondrial DNA (mtDNA) haplogroup

I (album), the debut album of Kurt Nilsen

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