From their website:

Many languages, one name: ISO

Because “International Organization for Standardization” would have different acronyms in different languages (IOS in English, OIN in French for Organisation internationale de normalisation), its founders opted for the short form “ISO”. The story goes that ISO is derived from the Greek word “isos”, meaning equal.

Whatever the country, whatever the language, we are always ISO.

https://www.iso.org/about