The '''International Organization for Standardization'''. 
It is to standards organizations worldwide what the [UN] is to the national governments.
See: http://www.iso.org for more details.

Sometimes this acronym also means ''In Search Of''.

----

From an [open source] perspective, the ISO unfortunately is an old-economy standardization organisation, i.e., they won't let you read their publications unless you buy them. Standards effectively available from other sources includes
   * ISO/IEC 10646 ([Unicode]) from http://www.unicode.org/.
 
----
[Category Glossary] (although ISO works as an acronym in some languages, their website claims the name is really derived from the Greek word ''isos'')