Why is the word "business" used in business rules? I'm migrating this question from SQA. Why do expressions like business analyst, business intelligence, business rules, etc. using the word "business"? I guess that is because usually software is ordered by a customer coming from a certain industry and for them it makes sense. But to me, the word "business" evokes ideas of accounting, sales, trading and similar. Maybe it is a dumb question. If so, please close it. I'm not a native English speaker and "business" just seems muddy sometimes.

The reason is exactly as you guessed. "coming from a certain industry and for them it makes sense."
If you look up the definition of the word "business" in say Merriam Webster's online dictionary you will find multiple definitions. The first listed by Webster more closely matches the ideas you think of when you encounter the word, but the second: "ROLE, FUNCTION" perfectly matches in this context...

The Business Rules lay out the purpose for some process, i.e. what ROLE or FUNCTION it serves.
Business Analysts analyze those processes to eke out both the abstract and specific rules...