Acronym for International Organisation for Standards. The acronym is a compromise between the English and French versions of the full name.

Also often used as a synonym for CDROM image files, because they usually have an .iso extension, stemming from to the ISO 9660 standard which specifies the CDROM FileSystem.

Some well-known (and some less well-known but commonly encountered) ISO standards include:

ISO 639:
Short names and two-letter codes for languages. Lists can be found here.
ISO 646:
A first attempt at internationalization of ASCII dating back to 1972. Specifies various tables which follow the ASCII mapping but replace a number of codepoints with accented characters. The list of replaced codepoints is 35 (0x23), 36 (0x24), 64 (0x40), 91-94 (0x5B-0x5E), 96 (0x60), 123-126 (0x7B-0x7E) (ie #, $, @, [, \, ], ^, `, {, |, } and ~). ISO 646 gained limited acceptance, but had obvious problems, and was later superseded by ISO 8859.
ISO 3166:

Short names and two-letter codes for countries. Used among others for the 2 letter ccTLD names such as .nz, .uk or .de. You might be able to find the list on a GNU/Linux system in /usr/share/zoneinfo/

Note that the ISO 3166 code for the United Kingdom is GB, not UK. This is the only exception to the correspondence between ISO 3166 country codes and ccTLD assignments.

There was a minor kerfuffle in 2003 when some ISO staffer proposed charging royalties to anyone using the 2-letter codes in their business, although those plans were quickly dropped following the predictable outcry.

ISO 8859:

A list of 8-bit character encodings extending ASCII for various European alphabets.

There are several ISO 8859 related ManPages; their wiki copies need some work, since there are duplicates...

ISO 9001:

Quality management systems. Specifies procedures for standardizing business processes to achieve consistent quality.

The important thing to remember about ISO9001 is that it's perfectly OK for an ISO9001 shop to fling completed motherboards frisbee style across the warehouse so that it hits the wall and lands in the pile for packaging/shipping as long as that is the written procedure.AsSeenOnSlashdot

ISO 9660:
The CDROM FileSystem. iso is also usually the extension used for CompactDisc images.
ISO/IEC 9899:
The international standard for the C programming language.
ISO 10646:
Essentially Unicode. See A short overview of ISO/IEC 10646 and Unicode, utf8(7) and UnicodeNotes for more information.
ISO/IEC 13346:
Universal Disk Format.

See also: TokyoDeclaration