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The Roman number for 4 (number). There are also separate Unicode characters for this number, 0x2163 "" and 0x2173 "ⅳ").

Côte d'Ivoire: NATO country code; from Ivory Coast.

InterVarsity Christian Fellowship: A Christian ministry for college students.

"Inter vivos": In law, as in inter vivos trust.

Intravenous: In medicine, as in "IV drip" (or simply "IV") for intravenous drip, or "IV drug use" for intravenous drug use.

Isla Vista: An unincorporated community near the Santa Barbara campus of the University of California, home to thousands of UCSB students.

Instrumental variable, a statistical analysis method

I've: In instant messaging slang, a shortened version.

Led Zeppelin IV: Possibly Led Zeppelin's most famous album, containing the song, "Stairway to Heaven."

IV (Cypress Hill album): The fourth album of west coast rap band Cypress Hill.

IV (Godsmack album): The title of Godsmack's fourth album.

IV (To/Die/For album), an album by the Finnish gothic metal band To/Die/For.

IV (Veruca Salt album): Fourth album by band Veruca Salt.

IV, shortform for Industrievereinigung Federation of Austrian Industry.

Subdominant scale degree, chord, or diatonic function: In music, when distinguished IV = major and iv = minor.

Current-voltage: In electronics where current is given the symbol I and voltage is given the symbol V.

Initialization vector: In encryption, a nonsecret binary vector used as the initializing input algorithm for the encryption of a plaintext block sequence to increase security by introducing additional cryptographic variance and to synchronize cryptographic equipment.

the Filename extension for Virtual Reality files.