ISO is the short name of the international body that writes shared rules for how goods, measurements, and technical things should be made and described, so a part from one country can match a part from another. Its full name is the International Organization for Standardization. Though actually, many English speakers — and some learner dictionaries — expand the letters as International Standards Organization, which is the tidy wrong name that the letters look as if they should spell. The group has national members in far more than the seventy countries older books still quote. You meet its work when paper is called A4, when a firm says it is ISO 9001, or when a camera setting is called ISO: those uses are rules the body published, and people often say ISO as if it were the rule or the number itself, not the organisation. In careful talk, ISO is the body; an ISO standard is one of its documents. People also call a disc-image file an ISO, from the ISO rule for how data sit on a CD; that is a stretch from this name, not a second organisation.