That invaluable tool, the Wikipedia, has the cleanest and concise definition of the term 'business rule' I've encountered. The Wikipedia defines business rule as:
From humble beginnings in the 1990s, business rules technology evolved into commercial-grade platforms capable of driving big and complex systems for Fortune 500 companies. Some technical infrastructures cost millions of dollars to implement and deploy. Business rules technology has become essential to the functioning of core business processes.
"Well, remember that what an ideology is, is a conceptual framework with the way people deal with reality. Everyone has one. You have to -- to exist, you need an ideology. The question is whether it is accurate or not. And what I'm saying to you is, yes, I found a flaw."
- Alan Greenspan
"This model will be a simplification and an idealization, and consequently a falsification."
- Alan Turing